I visited the incredible Basilica Cistern in Istanbul, a masterpiece of Byzantine engineering. Built-in the 6th century during Emperor Justinian I’s reign, this vast underground water reservoir once stored water for the Great Palace. Stepping inside, I felt transported back in time, surrounded by 336 marble columns, each standing 9 meters tall. The subtle lighting creates an atmospheric effect, reflecting the shallow waters below. The Cistern's construction is extraordinary, utilizing recycled materials from ancient structures, including the famous Medusa heads used as column bases. As I wandered through, I marveled at the ingenuity of this ancient marvel, which was crucial for supplying water during sieges. Visiting this historic site was like stepping into a hidden world beneath Istanbul's bustling streets, a testament to the city's rich past.