Istanbul: get an Istanbulkart and use the ferries

The Istanbulkart, sold at machines in metro and tram stations, works on the metro, trams, buses, funiculars, and the city ferries, and it's far cheaper than single tickets. The ferries are the best ride in the city: Eminönü or Karaköy to Kadıköy on the Asian side costs about the price of a tea and gives you the skyline. Hand over a small tip of tea money if a vendor on board brings you a glass.