The Castle Hill of Buda is an the average 50-60 meters
over the level of the Danube, its main mass is built from marl, and it is covered by so called fresh-water limestone. This limestone strata has a 5 kilometer long cave system, what was established in the middle ages into a continuous corridor and built up into the second cellar of the houses of the Castle District. A part of this system, which is located 16 meters under the surface was for decades a visitable unique cultural and tourist spectacle around the world. The Labyrinth of Buda Castle, among the worlds 7 underground wonders is in the present time unfortunately closed, not visitable.