A 16th-century horror show built in a lovely Italian garden.

The final home of the legendary Danish sailor said to have lived to be 146 years old.

Erosion has transformed this sandstone boulder into a massive dune-filled cavern.

Near this coastal cave stands a small memorial to the hermit who made it his home for three decades.

This forgotten chalk mine was reopened thanks to a massive effort from the local community.

An immense cave that has served as an outlaw's treasure trove, an underground dance hall, a nuclear fallout shelter, and much more.

The largest underground pedestrian tunnel system in the U.S. mostly caters to the people working in the offices above, but provides a great, air-conditioned way to traverse the city.

A 90-year-old underground water reservoir offers a more industrial kind of tranquility.

A taste of Middle Earth, in the middle of the Bayou City.

This small park features a monumental fountain wall, providing a great photo opportunity in the middle of Houston.

A breathtakingly steep set of stairs is carved directly into the face of the sea cliffs of Bonifacio.

Built to defend Washington D.C. during the Civil War, this fort became a post-war nucleus for a thriving Black community.

The museum moved on, but the diorama remain.

On a remote island in the northern reaches of Lake Michigan, a museum of collectibles collides with a vintage toy store.

This sprawling farm was once a Cold War-era hideaway for the nation's top diplomats.

A bunker "with enough U.S. currency to replenish the cash supply east of the Mississippi" in the event of nuclear war now protects nitrate film.

The Virginia home of one of the signers of the Declaration of Independence is being preserved with a unique glass facade.

The ruins of an 18th-century mansion that was once named "Mistake" by the man who had it built.

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