This open-air mosaic gallery honoring an English artist took hundreds of volunteers more than seven years to create.

An unusual ode to the late Irish playwright, complete with a squiggly bust and coffin-shaped bench.

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

This coffee shop lies hidden beneath a historic church.

The barrel-made lookout from Shackleton's final ship is tucked away in the crypt of one of London's oldest churches.

A wonderfully eclectic Victorian aquarium lies in the basement of the Horniman Museum.

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

This Viking gravestone carved in a rare runic style was dug up from a London churchyard.

The "lost friend” is the most famous of the six moai statues that were removed from Easter Island.

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

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

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

The first tunnel to be dug beneath a river, repurposed as an art and museum space.

A naturally mummified 2,000-year-old man.

An small and easily overlooked archaeology museum chock full of Egyptian artifacts.

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

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

Catacombs turned marketplace.

The curios of pharmacist and collector Henry Wellcome.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

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

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

This churchyard arbor is surrounded by hundreds of gravestones placed there by author Thomas Hardy.