Cave of the Crystals

The Cave of the Crystals in Mexico hasn’t been fully explored yet and most of it is forbidden to visitors. The cave is extremely hot, with air temperatures reaching up to 58°C (136 °F) with 90 to 99 percent humidity and therefore without proper protection, people can only endure approximately 10 minutes of exposure at a time. In order to map it, spelunkers had to wear special refrigerative suits and could only go so far due to their suits overheating.