Molnár János Cave

The Molnár János Cave is a thermokarstic water-filled cave system. It is located in the Rózsadomb district of Budapest in Hungary.The deepest sections reach 100 metres, while the total length of explored sections is currently 5.5 kilometres. The cave mouth is just 200 metres from the Danube.In 2008, a cave lake was found there, with largest chamber roughly 86 metres long, 27 metres wide and 15 metres high.

Source: Wikipedia