Looking a lot like Superman’s Fortress of Solitude, this crystal cave was only discovered 20 years ago outside Pulpi, Spain. Found beneath a silver mine, geologists quickly realized it was not exactly a cave. At 160ft deep it was determined that this egg shaped cavern was actually one of the largest geodes known to exist. The selenite crystals are believed to have started growing through a self-feeding mechanism of salt provided by dissolving calcium sulphate. Geologists have yet to date the age of the crystals…