Cross the Continental Divide through an old railroad tunnel, and ride back to the top on a shuttle.

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

Experience the wonders of a pristine night sky in this landscape free from light pollution.

An abandoned theme park with a strange and tumultuous past.

Explore the flooded remains of a limestone mine in Kentucky.

Once one of the most polluted caves in America, now an environmental success story and a museum dedicated to caves.

You can climb to the summit of Black Mountain, as long as you sign the waiver.

Eight rare Corvettes are swallowed up by a sinkhole in Kentucky's National Corvette Museum.

An interesting decoration on this historic site, this weathervane comes with as many legends as it does questions.

Oriental bazaar in the heart of Sarajevo.

The place where World War I began.

These warring psychedelic crags commemorate an unsuccessful military operation.

Bridge that died in war and was resurected.

This cemetery features modernist statues as strange as its name.

Impressive sink holes fill this untouched old-growth forest in the Bahamas.

One of the deepest blue holes in the world.

The medieval center of the Islamic world was also once the seat of Saladin's sultanate.

Standing atop 2nd-century Roman ruins, this church is one of the oldest and most iconic in Old Cairo.

This ancient structure is widely thought to be the oldest intact pyramid in the world.

A remarkable feat of Victorian engineering across the Firth of Forth.

The location of the Bridge of Death and the Gorge of Eternal Peril in "Monty Python and the Holy Grail."

Designed to allow funerals to proceed over the River Dulnain.

Described by William Wordsworth as a "World of Wonder."

An exceptional engineering feat that facilitates the migration of salmon upstream during their breeding season.