London's old-school healing garden.

Fantastically decorated underground chambers built in the 1760s.

Art Deco and “Wrenaissance” mash-up, this recently restored royal residence has been home to kings and comes with secret monkey passages included.

Shakespeare, David Bowie, Dr. Who, the Saxons, Druids and Romans are all claimed to have all made their mark on these massive man made tunnels.

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

The sign at the garden gate reads: "These Plants Can Kill."

Historic medieval fortified city in southwest France.

Human-made caves excavated to hide a secret society of wealthy pagans.

A mud statue stands in the dark tunnels, seeming to hold up the weight of the city above.

You can crawl inside this atmospheric 5,000-year-old tomb.

A careful eye can find hundreds of dinosaur tracks running along the Connecticut River.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

A pair of slides and a tree-lined stair corridor have been an urban oasis for nearly 40 years.

River pirates, murderous bandits, and serial killers used this Illinois cave as their debauched hideout.

One of the last surviving C-97s sits in a field in front of a Wisconsin inn.

You won't find these curiously named passageways anywhere else in England.

Eat your Big Mac in a DC-3.

Once one of the world's great cities, Cahokia was a place of religious worship, trade and mass human sacrifice before being mysteriously abandoned.

Symbolic attempt to overcome the issues of life.

Modeled after the labyrinth in Chartres Cathedral, this small-town Indiana memorial labyrinth sits half a world away.