Galata Tower is a 650 year old, 67 meter tall stone tower. Built by Genoese colony as the tower of fortifications around Galata, but eventually used as fire lookout tower during Ottoman Empire. It rises on the northbank of the Golden Horn. It has a fabulous view of Golden Horn, Historic Peninsula and Bosphorus. The tower is open to public, so you can enjoy the view from the top (there are elevators). You can reach the tower by walking down the Taksim Square through Istiklal Street for 2 kilometers, and turning left downhill when reaching the Tunel circus (Please see the map).
At the top of the tower, there is a restaurant, cafÃ© and a nightclub where special Turkish and oriental shows are held. Click here to for more information and reservations.
You can get more information about Galata Tower on Wikipedia.