Hranice Abyss

The Hranice Abyss (Czech: Hranická propast) is the deepest abyss in the Czech Republic. It is located near the town of Hranice (Přerov District). The lowest confirmed depth (as of 27 September 2016) is 473 m (404 m under the water level), which makes it the deepest known underwater cave in the world. Moreover, the expected depth is 800–1200 m.

The Hranice Abyss was created by a collapse of the cave roof, which was eaten away by warm carbonic acidulous spring water in limestone.