This extraordinary Depression-era expenditure was modeled after a postcard of a Mediterranean hotel.

The Cold War-era "underground Pentagon" is a sprawling subterranean hideaway for the Defense Department.

In the bowels of a 19th-century brewery lurks a fine-dining restaurant offering an array of themed feasts.

What looks like a simple quaint estate in rural Pennsylvania was in the 18th century home to a small monastic community.

This elaborate towering structure was once famed for its revolutionary height.

These tourist trap caverns are said to be the former home of a legendary Pennsylvania Hermit.

This rare triple-jurisdiction drawbridge passes through Virginia, Maryland, and Washington, D.C.

A star fort along the C&O Canal in western Maryland that protected America in three wars.

A lawn full of retired spacecraft on display at one of NASA's first research labs.

This bug-eyed water wheel uses the power of the Sun to clean up Baltimore Harbor.

Sail through this subterranean show cave that is home to a legend that would go on to name nearly everything around it.

Dedicated to the art and science of glass in equal measure, this space is as much laboratory as museum.

Contrary to what one might expect, ice forms inside this small cavern during the summer and melts during the winter.

This lush forest valley was once mined for lumber to the extent that it was once nicknamed "The Pennsylvania Desert."

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

An astounding collection of medical specimens, including bits of President Lincoln.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

Collecting 700 years of mechanical death-dealing, the NRA's sprawling gun museum is a revealing testament to the American obsession with armament.

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

Captain John Smith thought these cliffs were amazing in 1608 but sharks thought so 20 million years before him.

This scenic Maryland park was the site of one of the worst prison camps of the Civil War.

A maritime museum holding the remains of Blackbeard's pirate ship.

Rediscovered after a century, the father of the American Navy was reinterred in something dredged up from Davy Jones' Locker.

A priceless collection of the Nation's cryptologic history.