4. Cave of Crystals (Mexico)
Recently discovered in the year 2000 in Chihuahua, Mexico, this cave is full of unusually large crystals that measure over 4 ft in diameter and 30 ft in height. These were formed due to a magma infusion which heated the calcium sulphate found in the water source.
Fun Fact: As the cave is extremely hot, people cannot endure more than 10 minutes of exposure. This is also the reason why most parts of the cave remain unexplored.