A miniature rainforest is growing inside of a Midtown Manhattan office building.

Captain America, Sub-Mariner, and the Human Torch were all born in this art deco Manhattan masterpiece.

A hidden bar inside an ad agency has a deliberately misleading name, so employees can stay late under pretext of paperwork.

A whimsical, but often overlooked clock in Park Avenue.

Finally, you don't have to be a pious Swedish seaman to relax like one.

Though the case is scorched and the buttons half-melted, this hardy handheld gaming device can still run a game of Tetris.

Hear the quietest sound from across the dome.

The final resting place to 300 Victorian-era pets hides inside the city park.

The signs of a long buried road can still be found hidden beneath a London sewer grate.

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

An easily overlooked stretch of ornate window fronts and gaslight lamps that could be right from the pages of Dickens.

This collection of illusory paraphernalia has been culled from the history of London's premier magician's club.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

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

This shop and gallery is a modern-day cabinet of curiosities, unassumingly positioned along an urban thoroughfare.

The library houses an incredible collection of some of the world's most impressive books and manuscripts.

This legendary stone is of unknown origin, and throughout history has been a literal touchstone for British leaders.

A Roman spa buried deep beneath the City of London.

Europe's largest community of crocodiles and alligators.

The first AIDS memorial chapel in San Francisco and one of only a few in the U.S.

With the touch of a button, you can read a randomly selected short story.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

This tiny museum's sizable collection is jammed into a former underground public toilet.

An encyclopedic collection of mammal penises.