The commemorative stone column conceals a secret laboratory.

An architectural oddity hides in plain sight on this iconic London bridge.

This marine reptile was discovered by one of the 19th century's greatest fossil hunters.

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

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

This one has sailed five times as far as Sir Francis Drake's famous ship.

Ship-sized kinetic sculptural fantasy.

Pop culture has helped to keep this iconic British building from being destroyed.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

Scattered throughout London are ancient remnants of the city's former bounding wall.

Eighty million natural history specimens call this gargantuan museum home.

A tower-like theater in the Swiss Alps built to withstand the high winds and avalanches of the mountain pass.

A whale rib was used to advertise the store by the arch that offered exotic goods from far away.

Pilgrimage site for star-crossed lovers.

High winds can make this one scary landing.

The capital of Cambodia is named after the hill on which this ancient temple complex stands.

Khmer Rouge's high security prison.

One of the biggest markets in Asia, under one of the continent's largest domes.

5,000 skulls in memorial to those killed by the Khmer Rouge.

A battle between nature and architecture in the Cambodian jungle.

Water-powered gadgets whirr to life in this quirky eco park.

A graceful natural rock formation stands astride the point where the Gulf of California meets the Pacific Ocean.

A pixel art killer whale is frozen mid-leap in this Vancouver square.

The humble tomb of an Argentine general, hand-built by his son using stones brought down from the Andes.