From Katabaş, near Taksim at the end of the tram line, both atmospheric old ferry boats and more modern catamarans known as sea buses depart regularly for the islands, with more frequent service in summer. Ferries cost 5 TL for a token (3.50 TL with an İstanbulkart) and take around 90 minutes (www.ido.com.tr/en). The faster sea buses cost 9 TL for a token (7 TL with an İstanbulkart) and take about half as long, but don’t run quite as late in the day (www.sehirhatlari.com.tr/en). On weekends in summer both the ferries and the islands themselves can be very crowded, so it’s preferable to visit during the week. If you’re planning on staying the night, most hotels also have cheaper rates on weekdays.
No cars are allowed on the islands, so you'll do most of your exploring on foot. The cost of horse-drawn carriage rides varies by distance. On Büyükada, a "short tour" (40–45 minutes) costs 70 TL and a "long tour" (70–75 minutes) is 80 TL, while a one-way ride to the Monastery of St. George is 30 TL. Fares on Heybeliada are 45 TL and 60 TL, respectively, for short and long tours. Renting bicycles (4–5 TL per hour; about 10 TL for the day) from one of the numerous bike shops on Büyükada and Heybeliada is also a fun (and more strenuous) way to get around. To get from one of the Princes' Islands to the other, hop aboard any of the several daily ferries or sea buses.