Punkva Caves

The Punkva Caves (Czech: "Punkevní jeskyně") are a cave system of the Czech Republic located north of the city of Brno, near the town of Blansko. The Punkva River flows through it. Part of it is the Macocha Gorge, its sinkhole is about 138.7 meters deep and also the deepest of its kind (light hole type) in Central Europe. 
It is a popular tourist attraction for casual visitors to the region, in addition to cavers and advanced technical divers.