The Secret World's Seekers (2010)

You have to go deep underground, along a winding path. You will crawl in the mud and in the cold, in your own sweat, which after a while will freeze on your skin. You will go from light to darkness to rediscover the light, the light in yourself... The first part of the three-part documentary series about exploring the underground in Slovakia will guide you through a tangle of incredibly narrow passages and at the same time a number of spacious underground halls of little-known caves. It introduces you to the admirable people to thank for discovering the underground riches beneath our feet. Rocky Stream, Štefanová, Eternal Robot, Cave of Dead Bats, Old Castle, Moon Shadow. (distributor's official text)

Unfortunately the movie The Secret World's Seekers is not yet available on HBO Max.