A century-old network of freight tunnels underneath the city's historic business district.

One of the few remaining relics of the meatpacking hub that made Chicago the "hog butcher to the world."

The 30,000-volume library is one of the world's most impressive poetry collections.

The unluckiest U-boat in the entire German fleet is now on display in a Chicago museum.

Each of these gorgeous, intricately decorated rooms is painstakingly crafted to the scale of 1 inch: 1 foot.

A hollow cement depiction of time's inexorable effect on the human body.

This set of three large, volcanic hot springs is a favorite haunt for intrepid divers.

This ancient cave is home to a museum, bar, and is filled with fluorescent minerals.

A small flooded ghost town with a few scattered structures remaining.

The notorious Wild West outlaw was raised in this unassuming abode.

A museum in rural Utah documents the history of the Japanese Americans who were forcibly relocated there.

Visitors to this library are in for a real-world education in modernist architecture.

This raised bulls-eye visible from space was the subject of an intense geologic controversy.

The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

A well-preserved Ancestral Puebloan ruin tucked beneath a desert cliff.

Giant pinnacles in the sun-scorched lands of Southern Utah have been nicknamed "white ghosts."

A house carved into a rock in the 1940s.

The fifth-longest natural arch in the world, and the longest outside China.