A strenuous, unofficial trail leads to spectacular views in one of America's most remote national monuments.

An oil baron's wild paradise and the winner of an ill-fated air race.

The highest waterfall between the Rockies and the Appalachian Mountains.

A dangerous narrow-gauge railroad once traced a route through this striking canyon.

Raised high above the Cimarron River, this 1,268-foot rail bridge followed a half-century of trainwrecks, bridge collapses, and an abandoned town.

This harrowing climb along West Virginia's jagged spires is one of the only Via Ferrata on America's east coast.

This underground cave located in the most barren reaches of Idaho is filled with ice year-round.

Civil War dumping ground for the bodies of terrorized Union sympathizers.

The world's largest mineral hot springs is home to a herd of bison, a free public bath house, beautiful mineral formations, and a terrifying swinging bridge.

Nature has shaped this drainage tunnel into the digestive tract of a mighty beast.

River pirates, murderous bandits, and serial killers used this Illinois cave as their debauched hideout.

Crystal clear lake with a shoreline of travertine located in a Colorado canyon.

Hike the ruins of a zoo that was shut down by an unsolved murder.

In a 345-million-year-old cave that's 200 feet underground, dinner awaits.

A former sanitarium where soldiers were sent to recover in the healing waters of hot springs.

A lava tube cooled to form this long tunnel that stays chilly even at the height of summer.

The world's largest man-made underground caverns offer unparalleled underwater wonders.

A small town garden is dedicated to a psychic dog with the most soulful eyes.

This 40-foot fowl marks the so-called "wild goose capital of the world."

The abandoned remnants of a little sanctuary for world peace that fell into disrepair.

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

Once an ancient sea, this landscape of rocky ravines is filled with the fossils of ancient marine life.

A rancher expanding a natural spring for his cattle came up with bones – lots and lots of them.

This small town Texas cemetery is said to be the burial site of a UFO pilot who crashed in the 1800s.