Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

A tongue-in-cheek arcade where the games are based on everyday life.

A cluttered and astounding collection of antiquities and curiosities.

This coffee shop lies hidden beneath a historic church.

A living memorial to the trees London lost during the Great Storm of 1987.

Victorian-era Londoners really wanted to believe this 17th-century cistern was actually an ancient artifact.

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

This landmark church concealed a crypt packed with bones that was discovered thanks to the London Blitz.

Buried for centuries, this hidden cellar is all that remains of London's medieval Whitefriars Monastery.

Head underground and take a tour of the city's working sewer system, and see the underground river Senne, which defined Brussels for centuries before being covered in the 19th century.

Dummies recreate radiological discoveries from history.

Only museum in the world devoted to bookbinding and book arts holds a permanent collection representing five centuries.

Once thought to be the mysterious work of a witchy prophetess, a well with unusual properties turns objects into "stone".

Iron Age grave stones and Viking burials, a short drive from Gothenburg.

In the remote high desert of New Mexico, a strange array of poles beckon fury from above.

A museum of alchemy and a basement laboratory all housed in an ancient building in a Gothic tower.

Mysterious craters may have been home to an ancient cult.

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

High on a hill overlooking Los Angeles lives a world famous, high power conical Tesla Coil.

The world's largest solar furnace uses 10,000 mirrors to concentrate the sun's rays to generate power.

Research station devoted to mysterious floating lights seen in a Norwegian valley.

Nondescript elevator doors open to reveal a stunning, surreal world.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

This folly built to commemorate an aristocratic victory over Catholic rebellion plays tricks on the eye.