This sinkhole in the Arizona desert is filled with carbonated, arsenic-rich water

Colorful sand dunes create a unique attraction in this part of Utah's red-rock country.

Bizarre lunar-like landscape with thousands of large stone "hoodoos."

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

This shallow pit was once used to send over 20,000 buffalo plummeting to their death.

Native Americans built this circle of stones, which was used to predict astronomical events.

A black sand beach where glacial fragments wash ashore and look like sparkling diamonds.

This eye-popping Icelandic crater lake is surrounded by red volcanic rock.

Beautiful hillside Vermont cemetery with amazing funerary art.

Thousands of American timepieces on display in the former clock-making capital of the country.

A railroad tunnel that, upon its completion, was considered one of the engineering marvels of the modern world.

A carnivorous plant paradise in a serpentine bog.

A large wind turbine installation in central Washington State is home to an extensive set of interpretive exhibits.

One of the last active volcanoes on the Eastern seaboard.

Home of a 28-foot tall stalagmite known as the War Club.

Spectacular mineral formations fill these caves, which have been used for everything from smoking meat to stashing illicit liquor.

This former fire tower found new life as a communications hub complete with a scenic overlook.

The original span of a high bridge across the deep Crooked River Gorge has been preserved for pedestrian use.

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

One part local history, 99 parts gruesome haunted house.

This bleach-white graveyard overlooking the ocean is accessed through a tunnel.

The world's brightest bioluminescent bay.

Ho Chi Minh's perfectly preserved body has been on display here since 1975.

Home of the unusual art of water puppetry, one of Vietnam's oldest curiosities.