One of the most fascinating buildings ideal to visit while there is no sun is Istanbul's oldest built tank of perfect proportions and ingenious structure. Basilica Cistern, known as the Yerebatan Sarayi, is the largest of several hundred ancient water reservoirs still lying below Istanbul. It served as a water reservoir for the Byzantine Great Palace and was built in 532 AD. The flooded basilica is unique with its beauty and incredible marble illuminated by red light. Pillars hides two large Medusa heads, two imposing sculptures from the earliest period of Constantinople. On the pillars is a painted ceiling, which is why it is called a cathedral or a basilica.

When you step under the ground in the Cistercian Basilica, underground acoustics, enchanting stone pillars, and mystical red light drawn you into the world so different from the tremendous liveliness that takes place somewhere above.