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

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

This former quarry is now a vibrant labyrinth of magical in situ sculptures.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

An arcade packed with a rotating collection of unique independent video games.

Once the tallest building in the world and the site of "the highest dinner ever held in New York" this building now holds the most expensive penthouse in the city.

The "Seinfeld" diner.

A tunnel once abandoned now thrives with graffiti art as an off-limits makeshift gallery.

Hidden in Central Park's Ramble is a troublesome cave buried just beneath the surface.

A New York garbage depot holds a secret collection of weird and wonderful refuse.

Try not to get slimed in Tribeca.

This beautiful building in the heart of Manhattan's Financial District was empty for decades.

A crumbling hospital from the 1850s on Roosevelt Island.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

Lyon's "Wall of the Silk Weavers" is one of the largest murals in Europe.

Lyon's miniature version of the Eiffel Tower was built as a statement in support of French secularism.

This hidden garden boasts amazing views of Lyon.

Antique cinematography artifacts fill this museum dedicated to the inventors of the moving picture.

A tiled, multi-level garden of survival in Lyon.

Monsters and miniatures are held in equal esteem at this wondrous museum.

For hundreds of years, automatons moving to metallic music have been marking the passage of time.