An underwater city for the dead.

A pair of slides and a tree-lined stair corridor have been an urban oasis for nearly 40 years.

Crypt mausoleum in cathedral's basement contains relics of third century Roman martyr, Saint Vibiana.

A hospital closed seemingly in the middle of operations, leaving behind fodder for horror films and ghost hunters.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

Olfactory delights in San Francisco's Botanical Gardens.

A lush green oasis in the middle of Chicago.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

Hidden beneath the streets of London is a secret subway that only carried mail.

Banksy gives themself artistic license with this piece of London street art.

Home to items never before seen by the public.

Where manatees are the snowbird vacationers in these balmy Florida springs.

Two stunning 17th-century libraries and a cabinet of curiosities.

The haunting "Hell House Altar" is one of the few remnants of an abandoned college that has been a magnet for local legends.

A hands-on traveling collection of the innovative devices of yesteryear.

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

A prohibition-style speakeasy takes up residence in the last Victorian residence in Hollywood.

The rocks in this arid basin leave trails of movement behind them.

Its buzzing collection honors vibrator history.

A taste of the macabre Tokyo's ritzy shopping district.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

An emporium for the weird, creepy, rare, and just plain gross.

Carnivorous plants, medieval aphrodisiacs, and the largest original wood structure glass conservatory in the western hemisphere.