A fire lookout atop a glacial pinnacle is reached by climbing three vertiginous flights of stairs.

Peek into a cave of giant, glimmering crystals.

It's safe—and permitted—to walk across these twin natural sandstone arches.

A century-old church is now a space museum with a treasure trove of Soviet space items.

An abandoned railroad tunnel is now filled with bioluminescent bugs.

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

A sinuous path among steep cliffs creates a stunning sight in southwestern Serbia.

What was once a bustling mining installation is now a bustling hub of contemporary art.

This bike path was sunk below water level for maximum wonder.

The entrance to this Frankfurt subway station looks like an old tram car crashed into the concrete sidewalk.

The busy transport hub is home to the tallest airport slide in the world.

Nine nice parcels of land along a flight path offer a quiet respite... until a plane soars overhead.

Located in the remote Monitor Valley, this travertine bowl contains a scalding pool of water.

Crossing this suspension bridge feels like walking through the sky, a fitting tribute to the head of the Apollo program.

Ride a boat through this magnificent underground world, which now doubles as a theater.

A mile-long navigable cave adorned with stalactites and stalagmites reaching up to 65 feet tall.

The largest cave shaft in the world is home to thousands of birds and popular with BASE jumpers.

A spring water stream jumps through a walkable "bridge" cavern and a narrow canyon.

If there's another drive-through golf-cart bar in a bat-filled cave on top of a mountain, we don't know about it.

Alien rock formations grown from the sands of an Australian national park.

Dinosaur eggs were first discovered at these fiery red cliffs.

One of the most extensive and well-preserved collections of dinosaur footprints in North America.

A trail of footprints discovered after a landslide was left not by the Devil, as originally believed, but by an early human ancestor.

Its eclectic exhibits range from the world’s first motorcycle to Luke Skywalker’s Land Speeder.