Most-visited and most-photographed slot canyon in the American Southwest.

The artist James Turrell is repurposing an extinct volcano crater as an observatory to experience the cosmos.

The rodent-shaped sidewalk imprint that earned worldwide media attention.

These millipedes glow not out of attraction, but as a not-too-subtle warning.

Quite simply the largest tree in the world (by volume).

This small chapel is built of human bones and decorated with a golden skeleton.

This unassuming chapel in Portugal plays host to a ghoulish collection of bones.

Perhaps the most spectacular grotto along the Algarve coastline.

A once-booming Mississippi River town with a history of racial violence is now eerie and mostly abandoned.

Once used to protect important Roman trade routes.

The city of Manchester quietly unveiled this tribute to a 19th-century massacre.

This building's name and a plaque are all that's left of what was probably the most important nightclub of the Madchester music scene.

One of the best places to dig—some say on the planet—for six different types of chalcedony.

Two tall rocks sit at the center of this site, once the home of a large Ancestral Puebloan community.

This towering volcanic plug stands out among the dramatic formations that dot this otherworldly desert valley.

The land is full of geologic eye candy, such as otherworldly spires, mushroom-shaped hoodoos, and prehistoric fossils.

An endless sea of white conical domes.

Egyptian treasure trove of fossils documenting the whale's transition from land mammal to sea creature.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

This giant boulder is pinched over a 1000-meter abyss by two mountains.

Walk 2,300 feet above the ground on the "Troll's Tongue."

The last standing piece of a famous Honolulu landmark.

For many years, the river that Julius Caesar led his army across into Italy was lost until re-identified.

If you don't look closely, you might mistake this sculpture for just another passenger waiting at the airport.