Cold War paranoia built this hole. From 1963 to 1987, the Titan II ICBM Launch Complex 373-5, buried deep in the dirt near Pangburn, Arkansas, stood ready to vaporize a Soviet city at a moment's notice. Inside the silo sat a 103-foot missile topped with a nine-megaton W-53 nuclear warhead. That is nine million tons of TNT. Crew members from the 308th Strategic Missile Wing lived in a subterranean concrete capsule, breathing filtered air and staring at control panels, waiting for the launch keys they hoped they would never have to turn. But they kept their fingers ready. The silo itself was a marvel of defensive engineering, boasting steel-reinforced concrete walls several feet thick and massive spring shock absorbers designed to keep the electronics functioning even if a Soviet warhead detonated nearby.

Then the Cold War ended. Under the Strategic Arms Limitation Talks, the military systematically decommissioned these underground fortresses, stripping out the valuable guidance computers and pouring concrete over the launch ducts. Site 373-5 survived the purge in a weird way. Instead of obliterating it entirely, workers filled the access portals but left the physical layout of the complex largely intact beneath the Arkansas topsoil. It is a massive graveyard. It earned its spot on the National Register of Historic Places because it remains one of the best-preserved examples of a launch facility that could have triggered the end of human civilization with a single command.