Cave of Crystals:Spelunking never looked so good BBC
Silver miners first discovered Mexico's surreal Cave of Crystals almost a decade ago. The BBC recently took a rare tour of the underground cavern that contains the world's largest naturally grown crystals, where some selenite structures reach almost 33 feet in length.
See those little dots climbing the crystals that look like ants? Those are people.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.