One of the Seven Wonders of the Modern World holds the world's tallest metal staircase.

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

Every equinox this Maya pyramid puts on a spooky ancient light show.

Part of a WWII submarine is lurking outside the Washington Navy Yard parking lot.

Before Nixon, "watergate" meant canals.

The national park was once a plantation estate.

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

As the Dead Sea continues to deplete, massive sinkholes open along its banks.

This spiny beast guards an artist's village while vying for the title of largest lobster in the world.

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

This unique historical monument features large concrete spheres designed to resemble fallen stars.

Walk the whole Mississippi River!

A multi-storied adobe complex has been inhabited for more than a thousand years.

Yo, Adrian!

The iconic D.C. restaurant where the Cuban Missile Crisis was negotiated, now a Walgreens.

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

With nickel-steel armor and three-inch thick bullet resistant windows, FDR's train was a rolling fortress.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

There are lots of hands and feet stamped in the cement in front of Grauman’s Chinese Theater, but Mel left behind something extra.

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

Lie in a hammock where George Washington stood.

Genesis of modern hydroelectric power.

A building so large that it has its own weather.

Steepest flood safety railway in the entire world.