Basilica Cistern is one of the city’s most fascinating historical sites. Built in the 6th century during the reign of Emperor Justinian, this vast underground reservoir once supplied water to the Great Palace of Constantinople. Its dimly lit columns, silent waters, and famous Medusa head carvings create an almost otherworldly atmosphere. Over the centuries, it was forgotten, rediscovered, and restored, now standing as a quiet reminder of the city's layered past. Today, visitors walk on raised platforms above the water, taking in the history and engineering that kept an ancient city running.