The largest explosives factory in America once stood on land just south of Weldon Spring, Missouri. Ten years later, the same property was occupied by a plant that refined uranium for Cold War nuclear bombs. The site was abandoned in the late 1960s. Twenty years later, when the EPA showed up, what they found was a big, filthy mess.

What do you do with 1.48 million cubic yards of PCBs, mercury, asbestos, TNT, radioactive uranium and radium, and contaminated sludge and rubble? Rather than haul it west into a desert, the Weldon Spring management team hit upon a novel solution: they would entomb it right where it was, inside a man-made mini-mountain. 

Today, you can climb it as a tourist attraction.