In modern times, the Carlsbad Caverns were found by a teenager, Jim White, in 1898. He used a wire ladder like the one above to descend into and explore many of the rooms, the lower set of which are at least 1,027 feet below the ground. (There may be still lower chambers that haven’t been found yet.) The site became a national monument in 1923.

If you aren’t into stalactites and stalagmites, you can stop here.

Next: More otherworldliness, but above ground.