This underground cave houses the world's largest crystals

Mexico's Giant Cave of Crystals is home to the world's largest crystals. The beautiful but deadly cave, which is a horseshoe-shaped cavity, touches approximately 57 degrees Celsius with humidity close to 100 percent and almost no natural light, making it inhospitable. The cave contains selenite—gypsum crystals measuring up to 39 feet in length, almost as big as trees.