This simple rock stands as a memorial of the major student protests of 1968.

Also known as the Limete Tower, la Tour de l'Échangeur can be seen from almost everywhere in Kinshasa.

George Martin's Caribbean recording studio now rots within the shadow of an active volcano.

A short tunnel built straight through a magmatic dike.

A renovated hotel is bringing new life to a nearly-abandoned mining town in Colorado.

The only fully-realized skyscraper built by the famed American architect, Frank Lloyd Wright.

This massive underground salt mine now holds a sci-fi theme park in its depths.

Why walk on this historical site when you can zoom down instead?

This record setting conveyor belt system can even be seen from space.

Colin Stokes "got a bit carried away" and built a castle that looks like something out of Tolkien.

Secluded springs in the Rio Grande Gorge offer hot bathing beside the haunted ruins of a stagecoach stop.

An unassuming secret door once led to a legendary watering hole.

This large stone off the coast of Martinique had a brief career in the Royal Navy.

The sinister ruins of one of the worst dam failures of the 20th century lie in this astonishing alpine setting.

Over a thousand feet beneath the Detroit streets is a subterranean metropolis few are allowed to enter.

Visit the site of a subway powered by nothing more than air--and lots of it.

A group of college students hauled a desk up a mountain more than 40 years ago. The notebooks inside have become a makeshift time capsule.

A once-groundbreaking power plant turned into a hotel and mini-museum of archeological and geological wonders.

Take a steam-powered ride straight out of the past on this Appalachian rail line.

This lookout tower built in the 1930s is now an in-demand cabin with what might be the best view of the Seneca State Forest.

This hydraulic power system in London was, at one time, seen as a rival to electricity and the last of its kind to shut down.

Putting the "mod" in "modular" since 2000.

The first geometric self-supporting spiral stairs in Britain are a truly beautiful sight.

Swim or sail to this pie-slinging boat off the coast of St. Thomas.