This long, dark tunnel is open to hikers, but those without lights are known to get confused even on the straight path.

The rusting remains of the largest assembled WWII fleet on the West Coast.

Behind this beachfront shop lies a spectacular, colorful sea cave with an equally colorful past.

City Council meetings still happen in this historic building, impeccably preserved on the inside.

This monument on Breed's Hill proves that one of the most famous battles of the Revolutionary War is misnamed.

Concrete strongholds stand guard over the Golden Gate.

Another of California's unused Cold War missile defense complexes has become a graffiti gallery.

A building so large that it has its own weather.

A series of waterfalls and pools that flow through the 'Ohe'o Gulch and into the ocean.

This former luxury resort in Kaua'i is now an abandoned relic.

Take shelter from Hawai'i's tropical heat under the massive canopy of largest Banyan tree on the island.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

One of the world's largest Tesla coils.

100-year-old shipwreck you can walk up to at low tide.

Tubing through a cave lit with glowworms is a magical underground experience.

A miniature Italianate fantasy village on the coast of Wales and the set of ITC classic "The Prisoner."

Statue of Lenin, from Cold War era Czechoslovakia, now in a neighborhood of Seattle.

A giant Troll lurks under one of Seattle's oldest bridges.

From a neon Rapunzel to a bike traffic meter to a street fair color scheme, the most opened drawbridge in the US is a veritable art gallery.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

The world's oldest known salt mine.

A museum dedicated to the history and exploration of both popular music and science fiction.

Odd outsider art installations surround a Gold Rush-era ghost town.

The ancient tomb acts as a calendar that keeps perfect time.