Underground nuke tests

How do they do it? How far undergound do they do it? Is it like a huge hollowed out chamber in the earth or what... and do they have any way of overseeing the tests, ie a blast door with a peephole or something. kind of scary knowing there are a bunch of places like this across the earth that are just giant pockets of radiation. And wouldn't a huge blast in an airtight compartment be kind of dangerous, with the potential to make the earth explode from all the contained energy? Is there some kind of release valve?