Alabaster Caverns, Oklahoma (USA)

Alabaster Caverns is an Oklahoma state park that is home to the largest gypsum caves in the world. Entering through the entrance in the rock, you find yourself in vast well-lit halls 60 meters in diameter and 23 meters high. The walls are covered with a 50-centimeter layer of selenite, glass-like crystals. But most of the formations are alabaster - white, pink and black. Only two other veins of black alabaster have ever been found in the world - in Italy and China.