Known as the "Dodo Manège," this carousel features a herd of animals that have disappeared—or may be gone soon.

The history of radiation is on safe display at the foot of a radiation science laboratory.

A subterranean shelter remains intact under a busy Paris railway station.

A mechanized clock where a man fights off a dragon, crab, and rooster.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

Abandoned railway line circling the city of Paris.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

Bioluminescence in the reefs of the Maldives causes the sea to glow like a starry night sky.

These eerie outliers of the lightning bug family glow a mysterious blue color.

The cliff and rock formations are made out of Sioux Quartzite.

Abandoned silver mine strewn with wrecked and twisted structures.

The largest dinosaur trackway in North America is tucked away among this canyon's ghosts and archaeological gems.

Colorado's only true geyser is hidden within the San Juan National Forest.

The site of a defunct mill, that once supplied marble for the construction of the Lincoln Memorial.

Above Breckenridge, a destructive mining technique sits sunken in a small pond.

A miraculous natural phenomenon known as "the spring that breathes."

This sandstone building is a relic of the Overland Trail.

The only retired U.S. nuclear missile silo that is open to the public.

The world's largest carnivore sanctuary is home to over 450 meat-eating rescues.

One of the largest Buddhist stupas in North America is built of concrete designed to last 1,000 years.

This old train trestle and collapsed tunnel once allowed the railroad to negotiate the steep slopes of the Colorado Rockies.

These decaying bridges 1,000 feet high are a reminder of the skill it took to cross the Colorado Rockies by rail.

The first railway tunnel to cross the Continental Divide and, at 11,523 feet, was once the highest railroad tunnel in the world.