HAVE YOU EVER WALKED ON THIN AIR? Probably not. But you could come close if you were walking on this Slovakian lake’s unbelievably clear ice. Tomas Nunuk, a hiker from Bratislava, made this video of himself and a friend walking across the lake Velke Hincovo Pleso in Slovakia’s High Tatras Mountains. The ice is so clear that you can see straight to the bottom.

Commenters have, of course, been quick to doubt the authenticity of the video, but it is possible for ice to freeze this clear: if water freezes very quickly due to a sudden drop in temperature, it doesn’t get as cloudy. And Slovakia has recently experienced such a sudden drop in temperature. But it’s very rare that a lake’s ice would get this clear and be thick enough for a man to be able to walk on.