A "sinister, whimsical, tacky, and really orange" public art installation hidden under a Seattle bridge.

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

A replica that won't float away.

Once a menacing challenge for trailblazers, this trail is now the most scenic drive in Utah.

Florida castle built with aluminum printing plates.

One day a year it is legal to jump off of this astoundingly tall bridge that spans an Appalachian gorge.

Come for the speed, leave in love with the desert.

The hotel where Martin Luther King Jr. was shot is now a museum dedicated to his work.

19th-century operating theatre in which the use of ether was first demonstrated - plus, a skeleton and a mummy!

Walk the whole Mississippi River!

Fittingly, America's museum of architecture is itself a magnificently designed old building.

The fading, forgotten remains of a once bright and booming factory.

This concrete tangle of square pipes has stood as a proud thorn in the city's side since the '70s.

The unbelievably opulent home built for an infamous newspaperman.

Friction between grains of sand cause a curious "singing" sound.

Once connected to the outside world by a single train track, this ghost town is looked after by the National Park Service.

A modern ghost town whose inhabitants were driven away by the growth of nuclear power.

The largest drain hole in the world.

The first park built over a freeway is a brutalist masterwork.

During the holidays, a vintage subway train whisks New Yorkers back in time.

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

Yale University's home for rare works, including the mysterious Voynich Manuscript.

The flower-shaped temple in Virginia aims to transcend the boundaries of the world’s religions.

The only Bahá'í house of worship in North America and one of only a handful worldwide.