The bones of an old zoo crumbling in the shadow of a new one.

A spring-fed pool so deep it's used for scuba diving as well as swimming.

A vast city of the dead, where the deceased outnumber the living by more than a million.

Deadliest lake in the world suffocated over 1,746 people in one night.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

This ruined folly was originally built to honor a failed American state that would have become "Westsylvania."

World's smallest skyscraper, the product of a remarkable con.

One of the largest, oldest, darkest, quietest motel rooms in the world.

The "Prussian Versailles" that is as glorious today as when it was built.

The very center of Paris is surrounded by a bevy of strange good luck rituals.

An Art Nouveau building covered in animal gargoyles and grotesques.

Built in 1895, this bed and breakfast was once a hospital that served an early 1900s Gold Rush boomtown.

This one-of-a-kind archeological site is home to strange prehistoric ruins, the original use of which is still a mystery.

This palatial botanical garden is home to one of the largest pipe organs ever installed in a private residence, and a piece of Wood's cycad.

Established in 1638 to battle the Black Death, Hortus Botanicus Amsterdam is a treasure trove of rare flora.

The world's largest wooden trestle stretches across this desert canyon in Anza-Borrego Desert State Park.

A couple turned their front yard into an artistic masterpiece.

The first botanical garden, a feather in the cap of the Grand Duke of Tuscany.

Visible below the waves are memorials to the city's Gold Rush dead.

A 'living museum' in Leiden, the oldest of its kind in the Netherlands.

This cemetery served as the only official burial grounds in Cambridge for nearly 200 years.

A gravity-defying "devil's bridge" that has a surprising architectural feature for its stability.

An industrial relic is now one of Europe's most staggering art spaces.

The remains of centuries of copper mining appear like an alien landscape.