Istanbul is Turkey's most populous city, and its cultural and financial center. Located on both sides of the Bosphorus, the narrow strait between the Black Sea and the Marmara Sea, Istanbul bridges Asia and Europe both physically and culturally. Istanbul's population is estimated to be between 12 and 19 million people, making it also one of the largest in Europe and the world.
Istanbul was one of three European Capitals of Culture in 2010.

Understand

History

Expanding the ancient Greek colony of Byzantium by the order of the Roman Emperor Constantine the Great, the imperial city of Constantinople was for nearly a thousand years the last remaining outpost of the Roman (later termed Eastern Roman or Byzantine) Empire. It was finally conquered by the Ottoman Sultan Mehmed II on May 29th, 1453, an event often used to mark the end of the Middle Ages. It was the nerve center for military campaigns that were to enlarge the Ottoman Empire dramatically. By the mid 1500s, Istanbul, with a population of almost half a million, was a major cultural, political, and commercial center. Ottoman rule continued until it was defeated in WWI and Istanbul was occupied by the allies. When the Republic of Turkey was born in 1923 after the War of Independence, Kemal Atatürk moved its capital to the city of Ankara. However, Istanbul has continued to expand dramatically; today its population is approximately 14 million and increases at an estimated 400,000 immigrants per year. Industry has expanded even as tourism has grown. It continues to be a city that creates its own history at the intersection where both continents meet.

Orientation

Istanbul is divided in three by the north-south Bosphorus Strait (Istanbul Bogazi), the dividing line between Europe and Asia, the estuary of the Golden Horn (Haliç) bisecting the western part and the Sea of Marmara (Marmara Denizi) forming a boundary to the south. Most sights are concentrated in the old city on the peninsula of Sultanahmet, to the west of the Bosphorus between the Horn and the Sea. Across the Horn to the north are Galata, Beyoğlu and Taksim, the heart of modern Istanbul, while Kadıköy is the major district on the comparatively less-visited Anatolian side of the city. The Black Sea forms the northern boundary of Istanbul.

Climate

Climate	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Daily highs (°C)	7	8	10	15	20	25	27	27	24	19	13	10
Nightly lows (°C)	2	2	4	8	12	16	18	18	16	12	8	5

Forget the stereotypical Istanbul image of a city of 1001 Nights situated in the desert amidst date palms.
Istanbul lies on the same latitude as New York City to which it bears many similarities in climate and vegetation, as they both do not enjoy warm sea currents such as the Gulf Stream unlike the Mediterranean cities of Naples and Barcelona which also lie on the same latitude and are therefore much warmer and exotic in climate and vegetation than is normal for this latitude and for the very northerly Western Europe as well. And again unlike the stereotype it snows in the city, almost every winter — and a lot occasionally, although the standard wintry precipitation is rain and sleet.

It can be cloudy, rainy, or even snowy in Istanbul

Summer is generally hot with averages around 27ºC during the day and 18ºC at night. High relative humidity levels and the ‘concrete-island effect’ only make things worse. Expect temperatures of up to 35° C for the hottest days of the year. Summer is also the driest season, but it does infrequently rain. Showers tend to last for 15-30 minutes with the sun usually reappearing again on the same day. Flash floods are a common occurrence after heavy rainfalls (especially during summer), due to the city's hilly topography and inadequate sewage systems.
Winter is cold and wet, averaging 2ºC at night and 7ºC during the day. Although rarely below freezing during the day, high relative humidity levels and the wind chill makes it feel bitterly cold and very unpleasant.
Snowfall, which occurs almost annually, is common between the months of December and March, with an annual total snow cover of almost three weeks, but average winter snowfall varies considerably from year to year, and snow cover usually remains only for a few days after each snowfall, even under intense snow conditions.
Late spring (late May to early June) and early autumn (late September to early October) are very pleasant and therefore the best times to visit the city. During these periods it is neither cold nor hot, and still sunny, though the nights can be chilly and rain is common.
For visitors an umbrella can be useful to avoid the sun and rain. However, it’s not such a big problem, since streets of Istanbul are suddenly filled by umbrella sellers as soon as it starts raining. Although the umbrellas they provide are a little shoddy, going rate is only TL 5 –about US$ 3- per umbrella (though you can find much better umbrellas for that price at shops if you look around a bit).
Light clothing is recommended during summer. Bring a light jacket or sweater in case the summer evenings become chilly. Heavier clothing is essential during winter; bring a mixture of the two during spring and autumn.
Also take note that due to its huge size, topography and maritime influences, Istanbul exhibits a multitude of distinct microclimates. Thus, different sections of Istanbul can experience different weather conditions at the same time. For example, at the same moment, it can be heavily raining in Sarıyer in the north, mildly raining in Levent (northern terminus of metro line), while Taksim, the southern terminus of metro line, is having a perfectly sunny day.

Get in

By plane

Atatürk Airport

Most planes arrive at Istanbul Atatürk Airport (IATA: IST), 20 km west of the city centre. From the airport, there are various options for getting into Istanbul: you can take a taxi (about 30-35 TL to Taksim, and 25-30 TL to Sultanahmet), the express bus service run by the local airport service called "Havaş" which departs half-hourly between 4AM-midnight and costs 10 TL to Taksim (and also to Etiler, and Kozyatağı), the public bus (line #96T) run by İETT costing 2.50 TL, which also stops at Aksaray close to Sultanahmet. Travel times are 20–40 minutes, but depend a lot on traffic, and Istanbul is heavily congested!
Then, there is the metro (signposted "light rail" in the airport, when you get outside the baggage claim its about a 10 minute walk in the airport to the metro line. Just follow the signs), which will take you directly to the Otogar (bus station) or to numerous stops within Istanbul (Aksaray in the city centre is the last stop, transfer stations for tram heading for deeper into old city is available at Zeytinburnu and Aksaray). It costs 1.50 TL (+an extra 1.50 TL when boarding the tram) and getting to Aksaray takes around 45 minutes. It is possible to be at your bus departing from Otogar within less than one hour after landing by taking the metro.
When entering the metro station, you need to buy a jeton (token) for 1.50 lira. Just hand the cashier 1.50 lira and he'll give you a token, or use the automatic dispenser (Jetonmatik), which accepts banknotes (5 TL, 10 TL) as well as coins. They don't accept credit card or foreign currency here. This will get you on the red metro line (towards Aksaray). From this line, if you are going to Sultanahmet, you can transfer at Zeytinburnu and buy another jeton (1.50 lira). Note that the jeton token here is different than the first one. From Zeytinburnu, take the blue tram line T1, towards Kabataş which passes by: Sultanahmet, Eminönu and Tophane. The trip from the airport to Sultanahmet takes about 45 min.
Other Notes: Note that people are working on commission at the airport trying to make you use special shuttle buses for very high fees (30+ TL), so for people who wish to travel more economically the Metro/tram-combination is easy and fairly quick, and offers very good value. Travel by metro/tram cost 1 token per trip which is equal to 1.5 TL. No matter how long you travel, it cost 1 token per trip.
Visa: Depending on nationality, foreigners arriving in Istanbul may need to purchase tourist visas (USA and some EU citizens, depending on exact nationality, do). This must be done upon arrival before queuing for passport control. The windows for purchasing the visa are located immediately to the left of the main passport control booths. You may pay using foreign currency or Turkish Lira (TL) (only cash is accepted, though, no credit cards). The fee varies depending on the visitor’s nationality. The fee is $20 (or €15 or 10 GBP) for visitors traveling with U.S. and Australian passports. As of Sep 2008, Canadians pay US$60 (or €45). As of Aug 2009, EU pays €15 (note that GB citizens may pay in Pounds), or the fee is 35 TL.
Note that food and drinks at the airport may cost up to five times more than in the city proper, like in other international airports. If you are traveling on budget and plan to spend some time at the airport, it may be wise to bring your own meals from town instead of buying them there. If you come from the Metro, there is a supermarket in the tunnel leading to the elevators / stairs to the airport proper where you can do some last-minute shopping.

Sabiha Gökçen Airport

Istanbul also has a second airport, Sabiha Gökçen International Airport (IATA: SAW), located in the Anatolian side of the city. Charter flights as well as European low cost carriers operate from here most of the time. A Havaş bus connects this airport with Taksim in the city center for 13 TL (Dec 2010) and takes about an hour (closer to 2 in heavy traffic). There is also a Havaş service to Kozyatağı, a transportation hub of Asian Side, which costs 10 TL. If you arrive in the middle of the night, you can move to the departure hall after passing customs and rest on very comfortable seats — you will even find coin-operated Japanese massage chairs. Then, at about 4AM (but better ask to be sure) the first Havaş bus will take you to town. The Havaş bus schedule is sometimes linked to the arrival/departure times of planes. A cheaper option is to take public bus line #E10 which brings you to Kadıköy, the main centre of the city in Asian Side, in 70 min (3 TL) and which operates 24 hours a day (once every hour between midnight and 6AM, more frequent in the rest of the day). From Kadıköy, you can take a ferry to Eminönü or Karaköy. Various private operators offer internet bookable shared minibuses to central locations - a good choice when arriving late. A typical price being EUR 90 for 4 people to a hotel in Laleli. A taxi to Sabiha Gökçen airport from Taksim takes ~35 minutes at 3:30am with no traffic. The meter will show ~65 lira, plus there is ~6 lira in tolls. Note the security screening is before the check-in counters, so add some extra time to make the cutoff times (45 minutes for international, 30 for domestic).
When arriving at Sabiha Gökçen airport, there are people offering shuttle services to the European side of the city, most costing €10, which is much cheaper than booking a taxi with your hotel/hostel (about €50-60). It is the best option after the Havas airport buses. For the return journey, officers are quite zealous with luggage checks and they systematically remove the cap from bottled water once at the gate. It is recommended not to buy water before the flight although you can take the open bottle on board. Another surprising feature of Sabiha Gökçen airport is the luggage check at the main entrance, but fortunately you are allowed to take drinks in the airport at this point.

By train

International trains from across Europe arrive at the station in Sirkeci, close to Sultanahmet. Asian trains arrive at Haydarpasa station. To get between the two, catch a ferry across the Bosphorus (see Get around). Marmaray, the Rail Tube Tunnel and Commuter Rail Mass Transit System is being built, and is projected to be one of the most challenging infrastructure projects in Turkey.
International trains to and from Sirkeci:

Daily overnight train Balkan Express from Belgrade (Serbia) via Sofia (Bulgaria).
Daily overnight Bosphorus Express from Bucharest (Romania) (departure at 12.16PM from Bucharest, arrival at 8.30AM in Istanbul, but expect about 2 hours delay) Cost: 146 Lei (about 30 euro) for a second class sleeper. No restaurant.
TransBalkan Express from Budapest (Hungary) also has one of its cars attached to Bosphorus Exp. in Bucharest, thus providing a direct service from Budapest to Istanbul.
Twice a day there are trains to Thessaloniki (Greece) - the slow morning train that takes almost a whole day and the fast night train that is quicker but more expensive.

International trains to and from Haydarpasa:

Weekly trains to Aleppo (Syria) - taken out of service in 2008; it is unknown whether and when this service will resume.
Weekly train to Tehran (Iran) (from Haydarpasa station) every Wednesday 10.55PM, costing 105 Turkish lira. It is also a good way to drive in the Eastern part of Turkey. You change trains on Friday at Lake Van which requires a four hour ferry ride to get across. Both the Turkish and Iranian trains are comfortable and clean. Waggon restaurants are rather cheap. Arrival in Tehran on Saturday at 6.45PM (but expect up to 10 hours delay…).

Schedule and price list of railway trips can be gathered from TCDD (Turkish Republic State Railways).
When arriving at the Turkish border from Europe, you may need to buy a visa before getting your passport stamp. This counter accepts only Euros or USD, not Turkish Lira. You need to go to the visa counter first to purchase your visa, then to passport control to get it stamped.

By bus

Buses and coaches terminate at the colossal Esenler Otogar, about 10 km west of the city center, located on the European side. Courtesy minibuses or taxis will easily get you into the center. The metro also stops at the Otogar. There are several daily buses to/from cities in Bulgaria, Greece, Republic of Macedonia and Romania.
With 168 ticket offices and gates, shops, restaurants, hotel, police station, clinic and mosque, the Büyük Otogar is a town in itself. From/To Thessaloniki (Greece): ticket prices are around €35 (one way). From/To Sofia and Varna (Bulgaria): ~25€ (one way). From/To Skopje (Macedonia): ~40€ (one way)
"Harem" is the major hub for the buses on the Anatolian (Asian) side, which can be reached easily from the European side with a Ferryboat.

By boat

Maiden's Tower, located on an islet at the southern entrance of Bosphorus

International ferries, carrying tourist groups from outside Turkey stop at Karakoy Port. The port is ideally located close to Sultanahmet and Taksim.
Cruise ships often dock close to downtown. Passengers not on tours will find taxis readily available at the port entrance, and modern streetcars a short walk away.

By car

Traffic in Istanbul can be manic; expect a stressful drive because you will be cut off and honked at constantly. The city currently holds more than 1,500,000 automobiles and there is a strong demand for building of new or alternate highways.
If you've arrived in Istanbul by car, and you're not familiar with the streets, it's better to park your car in a safe place and take public transportation to get around.
The city, lying on two different continents and separated by the Bosphorus, is connected by two bridges. The bridge on the south, closer to the Marmara Sea, is called the "Bosphorus Bridge". The bridge closer to the Black Sea is named "Fatih Sultan Mehmet Bridge" and is longer than the first one. Both are toll bridges, and you must pay a fee to cross.
Since 2006, the Bosphorus Bridge toll stations do not accept cash, and payment must be made using electronic cards, either manually (KGS) or automatically via a transponder mounted on the front of the car (OGS). The Fatih Sultan Mehmet Bridge does not accept cash either, only KGS or OGS.
On weekdays, drivers should be aware of potentially hour-long traffic jams on the highways leading to both bridges, particularly heading west in the mornings and east in the evenings, since most people live on the Anatolian side but work on the European side.
There is a great shortage of parking in Istanbul, and existing lots are quite expensive. You will see many cars parked on the sides of the road, in front of garage doors even.
Drivers unfamiliar with the city should also be aware that street signs are rare. It is a common thing to pull over and ask for directions, something the natives and taxi drivers do quite often.

Get around

Public transport

Istanbul's public transit system can be difficult to figure out; maps are rare and you often have to transfer, and pay another fare, to get where you are going. However, if you put some effort into it, you can avoid taxis and not walk too much.
Each time you use a tram, metro, bus, or boat on the public transport system, you will need to use a token. The small metal tokens cost 1.75 TL (December 2010) and can be bought at various ticket kiosks at bus, railway and metro stations. Ticket fares across buses, trams and metros are at a flat rate (i.e. not dependent on how far you go). Only cash in Turkish lira is accepted at ticket kiosks of public transport, no credit cards or foreign currency.

Buying an AKBİL (AKıllı BİLet - Turkish acronym for "Smart Ticket") is a good idea if you are in Istanbul for more than a day or two, and intend to use public transport. AKBİL is a small electronic device serving as a ticket which may be used on buses, trams, suburban trains, metro, local ferries, etc. You buzz the AKBİL when you get on the bus or enter the tram/metro platform. The great part for travelers is that you can buy only one and buzz it as many times as there are passengers. You can buy or refill them at designated booths located at any major bus, tram, to metro station, as well as some other places such as newspaper stands close to bus stops. An AKBİL provides slightly discounted rates compared to regular single tickets, as well as discounts in transfers (when used multiple times within a limited period, roughly an hour and a half since the last time you used it). A deposit for the device itself is payable when you buy it (6 TL), which is refundable if you choose to return it later.
Buses and streetcars tend to be very crowded during rush hours, especially on Mondays and Fridays. That can also create opportunities for pickpockets.

By bus

There are two types of public buses in Istanbul; those run by the private sector and those run by the city-owned İETT. You can differentiate these two types by their colors. Privately run buses are blue-green with yellow non-electronic destination signs while İETT-run buses come in many flavors including old red-blue ones, newer green ones and red double-deckers. The Akbil Transit Pass is valid universally while tickets that can be obtained in kiosks near bus stops for 1.40 TL are valid only on İETT buses and cash payment only on private buses, although if you get on an İETT bus the driver will normally accept cash (normally 1.50 TL but this is dependent entirely upon what the driver wishes to charge) and hand you his Akbil for you to use.
Recently installed Metrobüs, long hybrid buses running on their special lanes separated from all other traffic and thus saving lots of time in Istanbul's usually congested roads, connect western suburb of Avcılar with Kadıköy in Asian Side via Bakırköy, Cevizlibağ which is just out of old city walls near Topkapı Gate, and Mecidiyeköy.
Most bus lines operate between 6AM and around midnight, usually with a reduced volume of services after 10PM. Some lines between major centres operate 24 hr, though, as is the Metrobüs, with about an hour intervals. After midnight, buses cost two tickets pp rather than the usual one.
24 hr Bus Lines:

73 Taksim Square-Ataturk International Airport
110 Taksim Square-Kadikoy
112 Taksim Square-Bostanci
25T Taksim Square-Sariyer
40 Taksim Square-Sariyer
89C Taksim Square-Basaksehir
E10 Kadikoy-Sabiha Gokcen International Airport
15F Kadikoy-Uskudar
130 Kadikoy-Tuzla
34A Sogutlucesme(Kadikoy)-Edirnekapi (Metrobus)
34 Avcilar-Zincirlikuyu (Metrobus)

As a tourist, you are most likely to use the tram and the metro in the Sultanahmet and Taksim area since there are no bus lines operating in the area anymore.

By metro

Istanbul's first underground system dates back to 19th century, when the funicular subway "Tünel" was constructed to operate from Karaköy to Istiklal Street in 1875. The distance travelled was 573 metres. Recommended option to go up-hill from Galata Bridge (Beyoglu side) to the famous Istiklal Caddesi (main street).
In 1990's, a modern tram line was constructed in the European side of the city, and now it's being extended to the inner parts of the city, as well as to the Anatolian side with a sea-tunnel named "Marmaray" crossing below the Bosphorus.
Istanbul's metro consists of two lines, the northern line is currently just a short stub connecting Şişhane to Maslak via Taksim Square, and Mecidiyeköy and Levent in business district. There is also a funicular system connecting Taksim to Kabataş where you can get on ferries and cross to the Anatolian side, and also transfer to trams bound for old city. The separate southern line is most useful for visitors, connecting Aksaray (with its connections to the tram line onwards to old city) to Atatürk Airport, via the main coach station (Otogar). A connecting line between southern and northern lines, crossing Golden Horn on a bridge, is under construction, but don't hold your breath.
Nowadays, most metro stations do not have a staffed ticket booth, so you will have to obtain your token from automatic token dispensers. Insert coins (except 1 or 5 kuruş) up to 1.50 TL and then press the button marked onay (Turkish for "approval", no English translations are given on the machines).
A token costs 1.50 TL (around €0.75) on any urban rail in Istanbul.

By tram

Istanbul Metro & Tram

A tram (line # T1) connects Zeytinburnu (connection to the metro line to the airport) to Kabataş (connection to the underground funicular to Taksim). The line is 14km long, has 24 stations and serves many popular tourist sites (e.g. in Sultanahmet) and ferries (e.g. Eminönü). An entire trip takes 42 minutes.
There are two tram lines running on the same tracks, the line numbered as 38 in front of tram cars runs along the entire T2 line between Kabataş and Zeytinburnu, while significantly shorter line #47 runs between Eminönü and Cevizlibağ stations (the latter of which is abbreviated as C.bağ-A.Ö.Y. on the signage of tram cars). However, both lines call at stations that are of most interest to travellers through the Old City. During morning and evening rush hours every alternate tram runs as #47, while during the rest of the day, most run as #38.
Although you may use the same tokens (1.50 TL) or AKBİL on the metro and tram, you must pay another fare each time you change lines.
The tram was put in service in 1992 on standard gauge track with modern cars, connecting Sirkeci with Topkapi. The line was extended on one end from Topkapi to Zeytinburnu in March 1994 and, on the other end from Sirkeci to Eminönü in April 1996. On January 30, 2005 it was extended from Sirkeci to Kabataş crossing Golden Horn after 44 years again. 55 vehicles built by ABB run on the line. The daily transport capacity is 155,000 passengers.
Tramway stations are: Zeytinburnu, Mithatpaşa, Akşemsettin, Seyitnizam, Merkezefendi, Cevizlibağ, Topkapı, Pazartekke, Çapa, Fındıkzade, Haseki, Yusufpaşa, Aksaray, Laleli (Üniversite), Beyazıt (Kapalıçarşı), Çemberlitaş, Sultanahmet, Gülhane, Sirkeci, Eminönü (ferryboats), Karaköy, Tophane, Fındıklı, Kabataş.
Between Taksim and Kabatas, there is a modern underground funicular to connect this tram line to the Taksim metro. The tram is also connected to the southern metro line (for the Otogar and Ataturk Airport) at Aksaray station, though the metro and tram lines are a short walk from each other.
During morning and evening rush hours (roughly between 7AM-9AM and 5PM-7:30PM respectively), tram cars run jam-packed so if you intend to take it for a couple of stations down the way, don't even bother—walking instead is not only less tiresome than standing in what is essentially more crowded than a sardine can, it's also quicker as you will most likely be able to get in the second or even third tram calling at the station due to the crowd.
There are also two other tram lines linking residential and industrial suburbs in the northwest with the city centre: T2, which heads for Bağcılar, and T4 (which is more like metro-tram systems of northwestern Europe, as it lies underground for part of its route), which heads for Sultançiftliği, connecting to the Zeytinburnu and Topkapı stations of the T1 line respectively. However, these lines are of very little, if any, use to the average traveller.

Information for disabled travelers

Buses

The process of replacing old buses with newer ones accessible for people using a wheelchair is ongoing. Many buses on central lines have a low floor and a built-in ramp (consult the driver to lean the bus down nearer to the ground, to open the ramp, and to assist into the bus, though any of these might unfortunately be impossible during peak hours in interval stops. Think of a sardine-packed bus unloading all of its passengers to lean down).
Unfortunately, no stops are announced on a display or by voice in the buses.

Trams

Trams are accessible for people using a wheelchair from the station platforms if you can manage to get into the station in the first place. Some of the stations are located in the middle of very wide avenues and the only access to them is via underground passages (tens of stairs) or overpasses (more stairs!). Otherwise, platforms in tram stations are low and equipped with gentle ramps right from the street (or sidewalk) level.
All stations are announced both on a display and by voice in the trams.

Metro

All stations and trains in the northern metro line are accessible for people using a wheelchair. Look around the station entrances for handicapped lifts/elevators. Only some of the stations in the southern metro line are equipped with such elevators (among the stations which have elevators are Aksaray-the main station of the city centre, Otogar-the main bus station, and Havalimanı (Airport) station), but whether there is an elevator or not, if you manage to get into the station (there is a good chance that you can do with a little assistance because the stations in the southern line aren’t located as deep as the stations of the northern line are; only about one floor’s height under the ground), all trains are accessible from the station platforms, though a little assistance more will be helpful for passing over the narrow gap between the train and the platform. You can ask the guys in grey/black uniforms (security guards, they can be seen in the entrances of the station platforms if not elsewhere) for assistance, it’s their duty.
All stations are announced by voice in the metro trains. In northern line it is also announced on a display, but not in the southern line. Instead, you should look at the signs in the stations, which are big and common enough.

By boat

Unique Istanbul liners (large conventional ferry boats), sea-buses (high speed catamarans), or mid-sized private ferries travel between the European and Asian sides of the city. The crossing takes about 20 minutes and costs 1.50 TL, and gives great views of the Bosphorus. Be aware that sometimes the ferry when arriving at a dock can bounce off the pier accidentally, even on calm days. This can cause people to fall over if they are standing up, so it is advisable to remain seated until the ferry has come to an absolute stop.
In Istanbul, liners from any given quay generally take only a certain route, and these quays are signposted ‘X Iskelesi’ (“X Landing stage/pier”). For instance, Eminönü alone has more than 5 landing stages (including the ones used by other ferries apart from liners), so if you should head for, say, Üsküdar, you should take the ferry which departs from ‘Üsküdar Iskelesi’. Replace ‘Üsküdar’ with the destination of your choice.
Istanbul liners travel on the following routes:

Karaköy - Haydarpaşa - Kadıköy
Kadıköy - Eminönü
Üsküdar - Eminönü
Üsküdar - Karaköy - Eminönü - Eyüp (The Golden Horn Route)
Kadıköy - Besiktaş
Kabatas - Uskudar - Harem
Istinye - Emirgan - Kanlıca - Anadolu Hisarı - Kandilli - Bebek - Arnavutköy - Çengelköy (The Whole Bosphorus Route)
Anadolu Kavağı - Rumeli Kavağı - Sariyer
Eminönü - Kavaklar (Special Bosphorus Tour-Recommended For Tourists)
Sirkeci - Adalar - Yalova - Cınarcık (The Princes' Islands Route)

Furthermore, the sea-buses (deniz otobüsü) follow the same (or more) routes, usually much faster than liners. Returning to Yenikapi from Kadikoy by sea-bus is a fast and convenient way to cross the Bosphorus; at Yenikapi there is a railway station with frequent trains to Sirkeci/Eminönü and the Yenikapi fish restaurant area is close by (or one stop on the train).
Four main private ferry routes for travelling between Asia and Europe sides are:

Besiktaş - Üsküdar
Kabataş - Üsküdar (close to tram and funicular system in Kabataş)
Eminönü - Üsküdar (close to tram in Eminönü)
Eminönü - Kadıköy (close to tram in Eminönü)

Very useful are the fast ferryboats (travelling at 55 kilometers) running from several points, such as the Yenikapi - Yalova one, that allows you (with a connecting bus in Yalova) to be in Bursa centre in less than three hours. Prices are marginally higher and the gain in time is considerable, though the view is not as nice.
All of the ferries, including private ones, can be paid for using the AKBIL system or the new Smart RFID Card that is in the process of introduction.
A new metro line extension crossing the Bosphorus in a tunnel is under construction. This will change the ferry provision and is perhaps a good reason to visit Istanbul before it is completed.