World's first "penitentiary," meant to be humane, drove men insane.

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

This dramatic rail curve was once the target of a failed Nazi attack.

You can walk through the first Boeing Air Force One, which famously carried JFK's casket from Dallas back to D.C.

An office built to look like a giant basket.

A favorite of Amelia Earhart, ranking among those rare bridges that can be crossed without changing sides of the river.

The tallest hotel in Europe.

This building holds the embalmed remains of the leader of the Bolshevik Revolution.

The gorgeous entrances into the city's underbelly look more like grand halls than subway stops.

Go inside to really appreciate this 500-year-old technological masterpiece.

This community on a small Venetian island has taken to painting their houses in bright neon hues.

Built on the remains of one the Incas’ most important gathering spots, this square keeps the spirit of a fallen empire alive.

A backdoor to Machu Picchu that only the most foolhardy infiltrator would attempt to breach.

The stones of this Incan wall complex fit together so well you couldn't fit a piece of paper between some of them.

If you’ve ever seen a picture of Machu Picchu, then you’ve seen a picture of Huayna Picchu—you just didn’t realize it.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

The eroded core of an ancient volcano is now accessible by a short hike.

A geological mystery on Camelback Mountain.

A Wild West jailhouse that slid down the mountainside.

Some of the tallest ancient American ruins continue to inspire awe and curiosity.

The world's largest military aircraft cemetery.

On the outskirts of a reborn ghost town, a decaying post office remembers the bad old days.

America's only nuclear missile silo open to the public.

An abandoned facility that has become a place of ritualistic satanic worship, or so rumor has it.