The Basilica Cistern is one of Istanbul's most wonderful tourist attractions. This tremendous, royal residence like underground lobby, supported by 336 columns in 12 rows, once stored the imperial water supply for the Byzantine emperors. The task was started by Constantine the Great but finished by Emperor Justinian in the 6th century. Many of the columns used in construction were recycled from earlier classical structures and feature decorative carvings.
The most acclaimed of these are the section bases known as the Medusa stones in the northwest corner with their Medusa head carvings. A visit here is very atmospheric with the columns beautifully lit and the soft, steady trickle of water all around you.