Icecap

Icecap, as this tower is known, was "the modular tower built for...a joint United Kingdom [and] Los Alamos National Laboratory undergound nuclear test scheduled for the spring of 1993," an NNSS fact sheet explains. "What was scheduled to be the 929th test came to a halt when President [George H.W.] Bush signed the Underground Nuclear Testing Moratorium on October 3, 1992."

Left as a monument to such tests, the 152-foot-tall tower "sits on top of a shaft which was originally drilled to a depth of 1,600 feet...The nuclear device would have been attached to the bottom of the rack and kept cold by using dry ice -- hence the name 'Icecap.' Subzero-degree air from the dry ice would have chilled the nuclear device to minus-42 degrees, simulating the temperatures a missile system would encounter in space."