The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

Along the most northwestern point in Africa is an ancient cave surrounded by legends.

Three small rooms at the back of the “official” church of London's clowns.

This hidden rooftop garden in downtown London offers a quiet respite from a bustling city.

A masterpiece of Art Deco architecture hidden in plain sight in West London.

The spot where three Protestant clergymen were burned at the stake during the reign of "Bloody Mary."

It celebrates a very stinky task and salutes London's fatberg-vanquishing team.

England's most famous front door has an accidental doppelganger.

A faded reminder of what was once a common sight in London during the Blitz.

A 26-foot shark sculpture—a statement about bombs—set off a municipal battle royale.

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

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

Black cat statues guard this temple-like Egyptian revival factory.

The sculpture of the deceased cockatoo flops atop its personal plinth.

The first geometric self-supporting spiral stairs in Britain are a truly beautiful sight.

These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

A relic of Victorian grandeur hides beneath a busy South London road.

19th-century scientists would make the pilgrimage here to verify the precision of their measuring sticks.

Collection dedicated to brands, packaging and advertising.

A network of concealed passageways lies within a busy London Underground station.

A Victorian natural history and ethnographic museum with wonderful turn-of-the-century, science-book-esque evolution displays.

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

Hear the quietest sound from across the dome.

In this cobwebbed old operating theater, you can practically hear the screams of the unanesthetized patients.