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

The largest cave chamber in Britain—big enough to fit a whole cathedral inside.

Hidden behind a wall for decades, this masonic lodge was only rediscovered during renovations.

This hidden green space is the city's second largest conservatory.

The television series' iconic giant foot was borrowed from this classical painting.

A collection dedicated to the treatment of disease, held in London's oldest hospital.

The largest of London's subterranean rivers and once a mad, bad center of London life.

One of the world's largest collections of pathological specimens.

A cluttered and astounding collection of antiquities and curiosities.

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

London's smallest police station is barely the size of a phone booth.

The remains of Crystal Palace Great Exhibition of 1851.

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

A historic London pub with prison cells in the cellar and a "spy room" on the second floor.

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

The anatomical-pathological collection of a man who changed surgery.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

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

A forest of immensely tall and unusually straight oak trees planted nearly 200 years ago to build naval ships that never came to be.

Legend has it that seven Anglo-Saxon kings were coronated on this stone, located in the appropriately-named town of Kingston.

A memorial to a dog that inspired rioting in the streets of London.

A beautiful Kentish country intersection hosts a tasty little photo spot.

You would never guess that before World War II this lonely field was a bustling German city.