This historic mansion was built as a symbol of love between a husband and wife.

The only recreation of William Shakespeare's indoor playhouse.

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

The highest point in Virginia can only be reached by passing through ponies and flowers.

America's first public mental health facility.

Exact replica of the ancient monument, but much, much lighter.

Outsider art meets paleontology at this roadside reptile repository.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

This stone memorial pays tribute to a massive shipwreck which was sadly overshadowed by the death of John Wilkes Booth.

Knoxville’s architectural icon was the symbol of the 1982 World’s Fair, even catching the googly eye of Bart Simpson.

A collection of huge Pre-Colombian structures in Alabama.

Golden Gate Park's historic collection of plants.

This private residence was the template for one of the most beloved television homes of all time.

An artsy hidden staircase leads to breathtaking views of San Francisco.

Before Nixon, "watergate" meant canals.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

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

An unassuming, powerful monument north of the U.S. Capitol bears witness to the resilience of Japanese Americans during a time of grave injustice.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

A nostalgic bibliographic gem.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.