Beyazit Kulesi (Fire Tower)
It was built by architect Senekerim Kalfa of the Balyan family in 1828 under the reign of Mahmud II. The tower is 85 meters in height and has four floors, 180 steps staircase to the top. It was built over the Golden Horn to detect fires in Istanbul, baskets during the day and large red, green and white lanterns in the evenings were hung on the tower to indicate that there was a fire in the city. It's still used for the same purpose today. Unfortunately it's close to the public at the moment, and stands in the grounds of University of Istanbul.