Built in the 6th century under Emperor Justinian I, the Basilica Cistern was the largest underground water reservoir built to supply Byzantine Constantinople. Spanning 9,800 square meters, it once held roughly 80,000 tons of water.

Supported by 336 marble columns — many repurposed from earlier ancient structures — the cistern's most striking features are the two enormous Medusa head carvings in its northwest corner, whose origins and exact purpose remain a mystery to this day.

With its dim lighting, echoing water sounds, and haunting atmosphere, the Basilica Cistern is one of Istanbul's most evocative sites, located within walking distance of Soie Boutique Hotel, right between Hagia Sophia and the Blue Mosque.