Another great find from the site “Dark Roasted Blend“:

“In 2000, one of the most unusual and splendid caves was found in Mexico by miners. Located only a mile from an upthrust of magma, this cave is 112 degrees Farenheit and at 90-100% humidity, limiting greatly the amount of time explorers can spend in it. It is a spectacular cave, with gigantic crystal formations thought to be 600,000 years old.”

There’s a whole raft of totally interesting caves and the like listed. Well worth checking out.