Gigantic Hole In A Mountain!

This hole in the side of a mountain led to the biggest cavern I have ever seen with a huge underwater lake!! each hole was about 30 ft across and it dropped down down about 100 feet at the high one. UPDATE: we got inside and kayaked through this mountain! check out the footage here: https://www.youtube.com/watch?v=TFG7l-x60GQ&t=2s