California's own medieval Italian castle, authentic down to the 300-year-old iron maiden in the dungeon.

It’s not hard to see why the historic Peabody Conservatory of Music’s library has been described as a “cathedral of books.”

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

A semi-scholarly approach to sex.

A sharp bend in a dramatic river canyon cut through red rocks.

Most-visited and most-photographed slot canyon in the American Southwest.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

Surprisingly delicious Asian-style hot dogs.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

This abandoned Slovenian military barracks has become a punky-political art squat.

A whimsical bridge adorned with decorative dragons.

This one-time health resort was used by aristocrats around the world.

This massive subterranean fissure is known as the "underground Grand Canyon."

Two very green residential towers cleaning the air in one of Europe's most polluted cities.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

Macabre astrological automaton clock dating to the late 1400s.

A church of bones, decorated with 40,000 human skeletons.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

Canada's subterranean Cold War museum has doubled as a movie set.

These locks on North America’s oldest canal are named after a porcine rock formation.