İstanbul
The Basilica Cistern is an underground Byzantine water reservoir in Fatih, on Istanbul's historic peninsula. It lies about 150 m southwest of Hagia Sophia. It was built under Emperor Justinian I in the 6th century, on the site of a former basilica, which gave it its name.
The hall measures about 138 by 65 m and could hold some 80,000 m³ of water. Its brick vaults rest on 336 marble columns, set in 12 rows of 28. In the northwest corner, two column bases are carved Medusa heads: one lies upside down, the other on its side. The cistern opened to visitors in 1987. It closed in 2017 for restoration and earthquake strengthening and reopened in July 2022.
Take the T1 tram to Sultanahmet. The entrance is on Yerebatan Caddesi, opposite Hagia Sophia, with 52 steps down. Allow 45 to 60 minutes. Ticket rules changed in 2026, so check current hours and fees before you go.