As well as appearing in Guetemala, sinkholes are also ocean-bound. Dean's Blue Hole is the second deepest underwater hole, at 663 feet. Guillaume Nery is a freediver, a water based equivalent of a basejumper. He jumps into underwater sinkholes with no breathing apparatus, other than his lungs. This is him jumping into Dean's Blue Hole.

The video is heavily edited. He doesn't actually get to the bottom. But it's freaky. Awesomely freaky.