The largest stone circle in the world has ended up bringing up more questions than it has answered.

Kings Cross Station pays tribute to its role in Britain's best-selling book series.

France's most famous cemetery, with some of its most curious tombs.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

A haunting collection of the vanished and disappearing natural world.

The celebrated eyesore created by starry-eyed sweethearts.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

A beautifully eclectic mix of architectural styles.

Hoax, mistake, or evidence of dinosaurs in human times?

A battle between nature and architecture in the Cambodian jungle.

Limestone caves in the Cambodian countryside, once the site of genocide, now a place of peaceful beauty.

A quick and simple solution to Cambodia's train woes.

An L.A. traffic island where the faces of locals have been carved into massive granite eggs.

A pair of connected skyscrapers form this symbolic gateway.

Manhattan's Thirteenth Avenue was made on landfill then deliberately destroyed — apart from one small, obscure block.

Elevated freight railway turned wildly successful urban park.

An artist's cute bronze subway sculptures belie his violent artistic past.

This abandoned subway station can still be seen on regular commuter trips.

Great place to have a drink and a bite to eat in an atmosphere laden with New York's Bohemian past.

The most confusing clock in New York.

New York City's smallest piece of private property.

Ride the subways of yesteryear.

In the middle of downtown Brooklyn lies a 165 year old secret hidden right below the surface (closed to the public indefinitely).