The commemorative stone column conceals a secret laboratory.

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

This 11th century tower is said to be the oldest building in Oxford.

An extraordinary collection of scientific instruments - and Einstein's chalkboard - inside the world's oldest purpose built museum building.

Home to the most complete dodo remains known - one head, and one foot.

One of Europe's oldest libraries.

J.R.R Tolkien, C.S. Lewis, and other "Inklings" met at the Oxford pub to discuss the now legendary fantasy stories they were writing.

A replica of the steam engine that hauled Queen Victoria's Royal Train is on display at Windsor.

This pump on the bad side of Victorian London betrayed a horrifying revelation about the water supply.

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

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

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

Religious structure known for its sculpted details.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

The romance of early commercial flight still fills this Art Deco destination.

Rumor has it the hot dog stand was targeted by two Russian nuclear missiles.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

At 207 feet, one of the world's longest continuous escalators.

The oldest continuously occupied public building in the United States.

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

Decades before the scandal, this staircase on the river was a literal "water gate."