The largest natural travertine bridge in the world is nestled in a small canyon in central Arizona.

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

The most powerful laboratory radiation source in the world pulses with 1,000 times the electricity of a lightning bolt.

Thousands of pieces of art have been carved into the rock at the site of an ancient volcanic eruption.

Greenery cloaks this serene sculpture inspired by the famous Lost Gardens of Heligan.

This small beach park is littered with a collection of unique driftwood sculptures.

A cheeky name for an observatory visitor's center.

A museum that chronicles the history of the Nuremberg Trials for Nazi war criminals in the building where the trials were once held.

This abandoned coliseum was intended to be a grand Nazi rallying ground before it was halted at the end of the war.

A castle from the Holy Roman Empire that hosts traveling youth... in its stables.

One of the American Southwest's most extensive collections of Navajo rock art.

This gallery of prehistoric red ochre art lines the wall of a scenic segment in Utah's San Rafael Swell.

This institution celebrates the happy accidents of uncommon sticktoitiveness.

When waves crash onto this section of beach, the rocks sing a song.

This picturesque cliffside beacon no longer calls to sailors but shines once a year in honor of a famous shipwreck.

A collection of 1,300 accordions of all shapes and sizes displayed in chronological order.

One man's quest to save his town with a trail of record-breaking sculptures.

These Great Lakes sea caves accessible by boat in the summer turn into temples of ice reachable by foot in the winter.

Labor provided by Great Depression-era programs restored these 25,000 acres in Tennessee.

The world's longest known cave system.

These early tent-shaped grave coverings are unique to Appalachia.

Every day a troupe of pampered water fowl walk the red carpet to their favorite fountain.

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

An enormous natural sandstone bridge in Kentucky.