The Underground Cistern, also known as the Basilica Cistern, is a fascinating ancient structure located in Istanbul, Turkey. It was built in the 6th century during the Byzantine Empire, and it served as a water storage facility for the city.

The cistern is located in the Sultanahmet neighborhood, just a short distance from the Hagia Sophia and the Blue Mosque. It is a popular tourist attraction in Istanbul and draws visitors from all over the world.

The cistern is an enormous underground chamber, measuring approximately 140 meters by 70 meters, and it can hold up to 80,000 cubic meters of water. The roof of the cistern is supported by 336 marble columns, each about 9 meters high, which were salvaged from earlier Roman ruins.

One of the most famous features of the cistern is the two Medusa heads that are used as column bases. The origins of these heads are unclear, but they are thought to have been brought to the cistern from a nearby temple during the Byzantine period.

Visitors to the cistern can explore the dimly lit chamber and marvel at the columns and arches that support the roof. The water in the cistern is no longer used for drinking, but it is still present, and visitors can see fish swimming in the shallow water.

There is also a raised platform in the cistern that allows visitors to get a closer look at the Medusa heads. The platform is accessible by a set of stairs and is a popular spot for taking photos.

Overall, a visit to the Underground Cistern is a unique and memorable experience for anyone visiting Istanbul. The sheer scale and engineering of the cistern are truly impressive, and the mysterious Medusa heads add an intriguing touch of ancient mythology to the site.