Cave Varone and its waterfall are a rare geological phenomenon.
The falls has a height of almost 100 metres, and is sourced from the river Margnone, which runs beneath the valley of Ravizze and down to Lake Garda.
Its waters are fed by underground leakage from Lake Tenno into the mountain that then forms the waterfall.
You can find more information about the geology and history of the waterfall here: Cascata del Varone
(Text from waterfall website and Wikipedia)