Kőbánya cellar system

The Kőbánya cellar system or cellar system of Kőbánya, sometimes known to non-Hungarians simply as the Kőbánya Mine, or the Kobanya Mine, is an extensive network of subterranea, or underground spaces, in the 10th district of Budapest, in Hungary. It is considered to be the largest cellar complex in the country. The complex as a whole started as an underground limestone quarry in a wine-growing area of present-day Kőbánya in the Middle Ages.

Source: Wikipedia