A marine aquarium with an astounding variety of fish hides in the basement beneath the famous Palm House.

Where's a guy to go after a long, hard day at work?

Legend says these colorful, invasive residents are the descendants of birds released by Jimi Hendrix.

The commemorative stone column conceals a secret laboratory.

A labyrinth hides in plain sight at each of the city's 270 Tube stations.

Never actually a tree at all, this spot was the site of London's public hangings for nearly 600 years.

This luxury shopping lane has been protected by its own tiny police force for over a century.

Public access to clean drinking water was an instant hit among the masses.

This museum tucked below a charming cafe gives a brief snapshot of photographic history.

A little slice of Japan and its aesthetics in London's Holland Park.

A clock designed to run with perfect accuracy for 10,000 years.

A cluttered and astounding collection of antiquities and curiosities.

Scattered throughout London are ancient remnants of the city's former bounding wall.

An alleyway plaque is all that remains of the independent Texas' envoy that forgot to pay their rent for over a century.

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

Continuing the tradition of the dime museum in style.

Explore the History & Technology of Electronic Communication

Downtown Minneapolis mixed art and function by turning some of their sewer covers into works of art.

Two geological phenomena in one precarious locale: a towering stone window, and a deep blue void.

Burial grounds for more than 1,000 bodies deep under the modern town of Rabat.

142 ceramic steps become a mosaic once a year.

The biggest and deepest Cold War bunker open to the public can be found in southeast England.

Man-made cave with enigmatic carvings, some say made by the Knights Templar themselves.

This little-known hero has been protecting "The Fens" for close to 400 years, and now from its most powerful challenger yet: climate change.