After a short-lived attempt to bring America in line with the rest of the world, this road was left in metric.

America's only nuclear missile silo open to the public.

These unusual rooms on wheels are holdovers from the 1960s.

The oldest continuously occupied public building in the United States.

A man-made island in scenic San Francisco Bay.

The highest bridge in America was built for an almost unnervingly small amount of money.

One-of-a-kind museum inside the first Boeing 747-400 ever made.

Considered by many to be one of the most dangerous highways in Alaska.

After serving in World War II and picking up Apollo astronauts, this aircraft carrier has been turned into a museum overlooking the San Francisco Bay.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

The black lab that was voted mayor of a California town is forever remembered by a life-size statue.

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

A rare tour of a commercial jet assembly plant, held inside one of the largest buildings in the world.

Thanks to a quirk of elevation this gift shop produces magic doughnuts that are found nowhere else on Earth.

Prone to disastrous fires, the city of San Francisco has the Guardian, a fireboat gifted by residents, to watch over them from the bay.

An Aladdin's cave of old Silicon Valley tech.

From the Difference Engine to the Cray-1, all under one roof.

The headquarters of the semiconductor giant has a 10,000-square-foot museum.

An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

A reversed traffic signal that was once violently misinterpreted as a statement on British-Irish relations.

This Art Deco fortress in upstate New York gives Manhattan's vaunted examples of the style a run for their money.

A small metropolis of Pueblo cave dwellings have been carved right into the hillside of this national monument.

The Denver airport is guarded by a 32-foot-tall sculpture of a demonic horse.