The Cave of the Giant Crystals of Naica. Located in the municipality of Saucillo, Chihuahua, at a depth of 300 meters, the cave houses the largest selenite crystals in the world, dating back more than 250,000 years. Its interior is extremely hot, with air temperatures reaching up to 58°C (136°F) and relative humidity between 90 and 99%. Due to these factors, the cave remains relatively unexplored. Access is restricted, so it can only be viewed through photographs.