A partial tunnel blasted into a steep ridge is all that remains of a failed railway across Arizona.

The largest natural travertine bridge in the world is nestled in a small canyon in central Arizona.

Ninety feet off the valley floor is an ancient dwelling put under protection of the U.S. government by Teddy Roosevelt.

A plaque commemorates the spot in the Oregon woods where the first-ever Geocache was hidden.

This small museum gives visitors a chance to soak up the history of the "sponge capital of the world."

A luxuriant botanical garden below sea level.

Couple's personal collection of pinball machines turned public pinball museum.

An allegedly haunted mansion with a tragic, tawdry past.

A comprehensive collection of bonsai set in a beautiful campus.

This 22-acre botanical garden is home to the largest collection of rhododendrons in the world.

The tiny church offers succor to travelers driving by, but only eight at a time.

The site of the Wellington avalanche, one of the America's worst railroad disasters.

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

Train debris from the deadliest avalanche in United States history can still be found in the ravine where so many perished.

The illuminated falls are a gem in North Cascades National Park.

Gold, silver, copper, lead, and zinc were once extracted at this abandoned mine near Lookout Mountain.

Oregon's unexpected high desert, displaying layers of time in a colorful show.

This great stone guardian of the forest is a relic from the land's volatile volcanic past.

Native American burial mounds? Giant gopher dens? No one knows what created the Mima Mounds.

The eerie remnants of an ancient forest were hidden under the sand for centuries.

Formerly secret, precariously perched boulders.