This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

Other-worldly rock formations and ancient fossils abound in this unique stretch of Nebraska badlands.

America's largest man-made forest was planted in an effort to bring back the past.

Once a slice of Cold War-era military history, this museum is finding its future in the star.

European castle ruins in an American state park are actually the product of death and grief.

The famous boat that once ferried Bogart and Hepburn still floats in Key Largo after being abandoned for years.

Before becoming a public park, this spot was a shell midden, a fort, and an amusement park.

The crumbling remains of a 19th century fortess.

This abandoned Civil War fortress is slowly being swallowed by the waters of Lake Borgne.

Pirates had to be ousted from the land where this now ruined Louisiana fortress was built.

The crumbling ruins of this southern American fort have survived storms, war, and cults.

A grandiose octagonal home crowned by a large dome stands out among the antebellum mansions.

This ancient settlement contains some of the largest earthen mounds in North America.

The remains of one of America's first radiation testing grounds still rest ominously in a Georgia forest.

The largest earthwork effigy in the world.

This underground holding cell was forgotten for over a century and rediscovered in the 1960s.

This Pennsylvania cave holds evidence of the oldest known inhabitants of North America.

The largest burial mound in the United States holds the remains of prehistoric West Virginians.

A long-abandoned provincial prison left to crumble in the frigid air of Ontario.

An otherwise quiet campground becomes a bustling medieval town for two weeks every year.

These mouldering mansion ruins remember a time when the Catskills were nothing but luxury.

This ruined castle perched atop a rocky peak is a great place for a hike.

Underneath the city that invented pilsners are a series of historic tunnels that have been storing beer for centuries.

This fairytale medieval church in Poland originally spent centuries in Norway.