The location of this small park was once the site of an infamous public morgue.

Two stone columns flank the grand Venice square, but there were supposed to be three.

An extensive collection of reliquaries containing the bones of saints housed in the largest Catholic church in Venice.

Visit Europe's largest subterranean waterfall, carved by water from the glaciers of the towering peaks surrounding the valley.

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

A shrine on the shores of the Tigris.

An Albanian monument to the Communism that nearly crushed the country is now a crumbling wreck.

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

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.

Once home to seven different roller coasters, Glen Echo has undergone many transformations since its founding in 1891.

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

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

The Pentagon is so large that it was planned like a city, complete with internal highway infrastructure.

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

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

Largest Roman Catholic church in North America.

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

Need a hardcopy of the 50-title Code of Federal Regulations? This is the place.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

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

An overlooked memorial honoring the local Washington residents who died in World War I.

Look closely and you’ll notice that the color changes a third of the way up the tower.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

The national park was once a plantation estate.