There's no denying it: the Cave of Crystals looks and sounds like a fictional location – somewhere Superman might go to get away from it all. So we were surprised to discover that underground crystal forests like this are actually real, and not just the product of a comic book writer's imagination.
The giant crystals in these pictures were discovered by chance during excavation work in a lead and silver mine in the Mexican state of Chihuahua back in 1985. Their size and beauty left many shocked. Some claimed they were proof of the existence of aliens, who presumably used the 10-metre tall columns to carve crystal skulls for some reason. Another, slightly more credible explanation is that the crystals were the result of groundwater saturated in calcium sulphate that was heated by magma millions of years ago. Whatever floats your boat.
Before you start scouring TripAdvisor for tips on underground accommodation, keep in mind that the cave is too dangerous to visit. Even if you were to get past the heavy steel door protecting it from looters, temperatures inside are a sweltering 45 degrees, with humidity hovering between 90-100 per cent. Thankfully National Geographic went there for us, so we can all enjoy these crazy, otherworldly photos from the comfort of our air-conditioned homes.