The Serefiye Cistern, also known as the Theodosius Cistern, is located in the European part of Istanbul, in the Sultanahmet district, near the Hippodrome and the Basilica Cistern. It is an underground Byzantine-era reservoir connected to the water supply system of Constantinople. After restoration, the monument was opened to visitors as a museum space.

According to the most widely accepted dating, the cistern was built in the 5th century, probably during the reign of Emperor Theodosius II. The structure has a rectangular plan and stands out for its rows of marble columns supporting the vaults of the underground hall. Different types of capitals and the reuse of architectural details are noticeable in its design, which is characteristic of late Roman and Byzantine building practice.

For tourists, it is an opportunity to see a lesser-known but well-preserved part of the city's engineering history. Unlike the larger Basilica Cistern, here it is usually easier to observe the structure of the space, the columns, and the lighting system. A visit is especially interesting for those who want to better understand how everyday urban life was organized in Byzantine Constantinople.

Today, light and multimedia shows are held inside, highlighting the architecture of the reservoir without concealing its historical character. Before visiting, it is worth checking opening hours and ticket prices on official resources, as visiting arrangements may change.