The Cave of the Crystals is connected to the Naica Mine 980-feet below the surface in Naica, Chihuahua, Mexico. The main chamber contains giant selenite crystals, some of the largest natural crystals ever found, similar to the ones seen in Superman’s Fortress of Solitude. The cave’s largest crystal found to date is 39-feet in length, 13-feet in diameter and 55 tons in weight. It’s extremely hot inside, with air temperatures reaching up to 136° F at 90% – 99% percent humidity. The caverns are relatively unexplored due to these factors, as without proper protection, humans can only endure approximately 10-minutes of exposure at a time. The Cave of the Crystals was discovered by brothers Eloy and Javier Delgado. Continue reading for more fascinating images from around the web.