The Underground Mosque

As the Ottoman sources mention the Underground Mosque as Mahzen-i Sultani officially, and some other historical resources claim that it is a fortress named "Kastellion ton Galatau," According to Cristoforo Buondelmonti’s engravings, around the 15th century, this fortress was still here. While the siege of Istanbul by Fatih Sultan Mehmet the chain which was stopped Fatih’s ships to prevent from continuing Golden Horn was tied here. After the conquest of Istanbul, it was used for ammo storage, a water cistern, and lately, a mosque.

The tombs of the Islamic prophet Muhammad’s companions Amr bin al-As, Vehb B. Huseyre and Sufyan B. Uyeyne from Tebeu't-tabiin (there is no proof whether they were companions or not) are also here. It is considered the most visited holy place in Istanbul after Eyupsultan.