We sailed into Istanbul on the Celebrity Reflection for 2 days this summer. Others have posted extensively on navigating the city and the major sites which was helpful in planning our trip. I was very interested in visiting the Asian side but couldn't find much advise in that regard. This post is to help those figure out the ferry system who want to visit the Asian side.
Although the cruiseline offered cruises along the Bosphorus, none actually stopped on the Asian side. With advanced planning we were able to do this on our own. It's safe, inexpensive and easy. What I learned before going is that the company which operates Istanbul's official sea bus/municipal ferries is called Sehir Hatlari. Think about the municipal ferry lines like you would a subway or city bus system in any major city. Sehir Hatlari is owned and operated by the government just the same way. Many people live on the Asian side but work on the European side and commute back and forth each day by boat. It also operates the Bosphorus cruises, but if you don't have time/interest in one of those you can certainly just hop a passenger ferry between the 2 continents.
Ferry line stops and schedules are on their website at http://sehirhatlari.com.tr/en. They're clean, modern, and convenient. If you're going to do this, you can print out maps of the stops and corresponding schedules to help you determine where you want to go and when the ferries arrive/leave. The ferry stops are well-marked and all the people are very nice if you need help. TIP: They also have a mobile app which I downloaded on my phone in advance of the trip.
Here are 3 stops to help you get your bearings:
The Karakoy ferry stop is nearest where the cruise lines dock on the European side. This ferry stop is at the base of the Galata Bridge before you cross the Golden Horn.
The Eminonu ferry stop is on the other side of the Galata Bridge nearer the Sultanhamet (historic district) across the Golden Horn but still on the European side.
The Kadikoy ferry stop is just one town on the Asian side and the destination we'd planned to visit before leaving home. It was described as a lively area with up-market shopping, eating, and entertainment making it popular with wealthy locals.
Leaving Europe / Buying our Ferry Token / Boarding the Ferry
At the Eminonu ferry stop, we saw the building that said Kadikoy (our destination). You buy a token for your fare from a kiosk. The only difficulty we had with this, and what I hadn't prepared for, was that it was in Turkish. Luckily, a very nice man working a fruit stand saw we were having difficulty and actually ran over to help us. Like our own vending machines, the kiosk seems sometime temperamental with paper money. He kept flattening it out (a universal solution apparently) and had to try several times before it actually took the money. If you put paper money in, you'll get change back in coins. The ferry token and coins look a lot alike to the foreign visitor. He was nice enough to pull the token out separately and hand it to us. The token is slightly smaller. TIP: If you know you're going to return to the same stop, then go ahead and buy your return token at the same time.
After you have your token, just walk to the entrance (it's right there and can't be missed). Drop your token into the turnstile and just walk on the ferry. There's indoor and outdoor open seating and upstairs had a coffee stand selling food and drinks. We left from Eminonu and the fare cost us 1.95TL pp each way and the trip was about 15 minutes and provided breathtaking views of Istanbul.
Arriving in Asia / Returning to Europe
We got off the ferry in Kadikoy and there are people everywhere along with ice cream stands, etc. We walked down to the right a hundred yards or so along the promenade on the waterfront taking pictures. We came to a large square where locals were milling about, children playing in the square, and a large Turkish flag (more pictures). If you face the town with the water at your back and look straight ahead about 200 hundred yards, you'll see a Starbucks on the corner. We walked in that direction and spent about 2 hours exploring the narrow streets lined with shops, cafes, restaurants, stopping for Turkish coffee, browsing bookstores, etc. To return, we walked back to the Kadikoy ferry stop and this time looked for Eminonu. We could've also taken the Karakoy ferry if we were headed back directly to the ship.
On a related note, I can't stress enough how helpful the Turkish people are. We stopped numerous times to ask for directions to various museums, mosques, and other landmarks and each person was kind and encouraging. Although salesman were certainly interested in our business, we found them to be friendly in their persistence but never rude or aggressive.
I'm so glad we did this and I hope this helps others who want to do the same thing but who might be nervous. It was so easy to do and worth the little bit of effort to figure it out to say you actually stepped foot in Asia. Next time, I'm going to Asia for dinner!