Unique tower has outlasted a takeover of the company.

A painfully obvious spy house sits right across the street from the Russian Embassy.

The walls of the iconic dome are hollow and have a secret stairway.

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

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

The most accurate timepiece in the world.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

Despite being made of a seashell mortar, the crumbling remains of this historic Florida mill are still standing.

The third tallest lighthouse in America once guided author Stephen Crane to safety.

A sculpture of the famous photograph stands on San Diego's "Greatest Generation Walk."

This replica of the Greek structure is in the heart of Nashville.

Largest Roman Catholic church in North America.