Here is a little tour of a Sehir Hatlari Istanbul Ferry. The cost usually is around 2TL or about $0.75. The ferry takes you across the Bosphorus lines from the Europe to Asia side of Istanbul, where it is less touristy. I don’t quite remember the route, but I believe its Kadıköy-Eminönü. The total trip is around 15 minutes, the fun part is make sure bring some breads and feed the seagulls.