The remains of a military communications outpost still stand on this Greek island.

A commemorative plaque hides a door that leads down to the New York Public Library's underground book bunker.

The last SR-71 ever constructed.

A lone historical marker off the highway and scattered debris are all that remain of this Cold War-era missile site.

Dating back to the 1800s, two imposing buildings in Michigan have had countless transformations over the years.

These abandoned grain silos and tunnels are an urban exploration dream.

The watery grave of an impractical idea.

The superstar of Cold War nuclear bunkers has been featured in countless films but is now barely operational.