This artificial cave looks like something out of a fairytale.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

A steampunk-styled three-floor factory churning out art, activism, and electronic beats.

The hidden lair of an alchemist rediscovered in a 2002 flood.

Countless grotesque faces stare out from this eerie Prague art wall.

This bookstore serves recipes from the cookbooks on sale.

Only a few pieces remain of the structure that carried people and goods across the Thames for some 600 years.

Tucked away behind the mansions of Mayfair, this picturesque garden is a hidden London treasure with a spooky past.

Though it's not the largest, this one-kilometer outdoor market is reportedly the longest in Europe.

A mineral spring that became all the rage in 17th-century England.

A relic from one of London's worst 19th-century slums.

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

A fully functional, 200-year-old remnant of the time when Brixton was mostly fields.

The plunge pool is a surviving relic of a rowdy royal residence.

An archive of ceramic eggs painted to record clowns' personal makeup designs.

The commemorative stone column conceals a secret laboratory.

This beautiful deer park was built so King Charles I and his court could go hunting while escaping a deadly plague outbreak.

The wooden telephone box hidden away in London's Piccadilly was the original prototype of the iconic kiosk.

The ritual has been performed uninterrupted for nearly 700 years.

A domino effect created with Britain’s iconic telephone boxes.

There's an exclusive Beefeaters pub hidden in the Tower of London.

This unique bridge curls up like a caterpillar to let boats pass and then unfurls again to span a small canal.

This coffee shop lies hidden beneath a historic church.

A Roman spa buried deep beneath the City of London.