Running under an entire mountain, the longest highway tunnel in North America is kept fresh using portal fans and jet fans.

Secret North Korean passage discovered below the world's most dangerous border.

The former Naval shipyard is open for exploring - mostly.

A "haunted" landmark on the coast of Southern California.

This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.

Home to more than 13,000 pieces of war memorabilia and military equipment.

The spot in the Mile-High City that's exactly 5,280 feet above sea level (at least for now).

Come crisp December nights, this fairly plain neighborhood becomes a holiday dream world.

The tragedy of the Japanese internment camps is remembered here by a stark "Soul Consoling Tower."

The largest source of fossilized insects anywhere.

Commonly referred to as the most photographed Victorian home in the United States.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

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

An abandoned Jazz Age dream home and con man's hideout in Death Valley.

This immigrant bridge once spanned the Thames but is now a fixture of an Arizona city.

"Only the devil could play golf here."

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

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

Two mammoth statues inspired by equally tall tales lure tourists to this roadside attraction.

The land is home to swimming ponies and a legendary 18th-century treasure.

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

A downtown park built on top of unclaimed graves.

America's most famous piece of self-built architecture.

Concrete strongholds stand guard over the Golden Gate.