The Tapolca Lake Caves 

The Lake Caves
This 3 km long lake cave system is situated in the heart of the town. It was opened to the public in 1912, ten years after its discovery. Small boats can be hired to explore the cave system. At 15-20 m below the town, a 5 km long cave system criss-crosses the Miocene limestone layers. This includes the 3.3 km long Lake Cave, which is mostly filled with karst water.