The Denver airport is guarded by a 32-foot-tall sculpture of a demonic horse.

A planet-hunting astrograph built in the 1920s to seek out the so-called "Planet X" beyond Uranus.

Catch a ride through the Pennsylvania countryside on this historic narrow-gauge railroad.

The California capital city once stood 10 feet lower than it does today.

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

A beautiful Gilded Age hotel in the White Mountains with surprising diplomatic history.

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

This sign designates the road that leads to the infamous Area 51.

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

This massive subterranean fissure is known as the "underground Grand Canyon."

Dedicated to the art and science of glass in equal measure, this space is as much laboratory as museum.

The hallowed remains of a 900-year old Ancestral Pueblo great house.

This fast-food outlet is the only space and UFO-themed McDonalds in the world.

Inside this striking glass building, visitors can see thousands of dinosaur fossils in the positions that nature deposited them more than 150 million years ago.

This Moab institution functions as both a rock store and a small natural history museum.

A tunnel with windows, so you don't miss out on the impressive views.

A picturesque example of brute-force engineering conquering nature.

Before it was buried by volcanic ash, this fast-food restaurant fed the hungry hordes of ancient Rome.

If it hadn't been caught in time, a flaw in the design of this Manhattan skyscraper could have led to its collapse.

Home to the world's oldest wooden building.

Devoted Buddhists can earn enlightenment in the next life by crawling through this symbolic nostril.

This massive wooden building contains a giant Buddha, healing pillars, and tame deer wandering the grounds.

Considered by many to be one of the most dangerous highways in Alaska.

This public space is speckled with the eerie remnants of a defunct amusement park.