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

A stone arch leads to a cavernous 1930s spring house tucked away in the Pennsylvania woods.

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

The Grand Canyon of Texas.

Despite time, colonization, and the brutal New Mexican heat, these Pueblo ruins still stand.

This fantastical waterfall is hidden in a cave located in a cracked cliff.

Garden dedicated to native carnivorous plants and site of huge flytrap heist.

This massive subterranean fissure is known as the "underground Grand Canyon."

A miniature train-ride through Slovenia's largest cave system.

An eerie and beautiful group of columns mark the site of a grand mansion lost to time and fire.

These spectacular ruins were built by Spanish padres in the 17th century.

A luxurious 1880s hotel with its fair share of Tiffany stained glass, Edison electricity, and of course, ghosts.

The one-stop shop for all of your superhero (or evil arch-nemesis) needs.

Connecticut grave of the woman responsible for the Winchester Mystery House in California.

A remote desert lookout offers unparalleled views of the California badlands for those who brave the trek.

A small sculpture garden that provides a microcosmic representation of California.

A raised boardwalk winds through a thicket of stunted, century-old trees no more than nine feet tall.

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

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

The great Italian Renaissance painter was laid to rest here in the Chapel of Saint-Hubert.

Guests can stay at a hotel in the former French abbey where lie the tombs of King Henry II and King Richard the Lionheart.

The medieval castle built as headquarters for the Pope's secretive Knights Templar.

A hidden tunnel leads to an abandoned slate quarry that's now a secret swimming spot guarded by cliffs.

The jewel of western Mexico's archaeological legacy is this tiered circular pyramid now covered in grass.