Picture a glittering crystal palace buried 1,000 feet underground, filled with translucent pillars the size of school buses. Now imagine that stepping inside, unprotected, will kill you in about 10 minutes.

This episode descends into the Cave of the Crystals (Cueva de los Cristales) in the Naica mine of Chihuahua, Mexico — a fleeting window into an alien world that humans uncovered by accident in 2000 and lost again in 2015. We unpack the geology that grew the largest natural crystals on Earth, the extreme technology it took to survive inside, and the half-million-year-old life found sleeping in the stone.

• How a fault sitting above a magma chamber acted as a "slow cooker," growing selenite crystals up to 37 feet long and 12 tons over 500,000 to 1 million years.
• The deadly physics of 136°F heat at 99% humidity, where evapo ...