Moravian Karst

The Moravian Karst is a karst landscape and protected landscape area to the north of Brno in the South Moravian Region of the Czech Republic. It encompasses a number of notable geological features, including roughly 1100 caverns and gorges and covers an area of roughly 92 km². Currently, five of the cave systems are open for public tours; another - Amatérská Cave, Býčí skála Cave or Stránská skála only for science exploration.

This region is also home to one of the most important single geological features in the Czech Republic, the Macocha Abyss, a gorge 138 m deep, which was formed when the ceiling of a cave chamber collapsed. Macocha Abyss is also the place where the Punkva River begins to run underground through the Punkva cave system, and two small pools of water are visible at the surface.

Source: Wikipedia