Locally known as the "Onion” and the "Egg Beater,” Casper’s most recognizable buildings are beloved local landmarks to many, and eyesores to others.

This ruined fort and statue are a testament to the last king of Kaua‘i’s savvy diplomacy skills, which briefly brought Russians to Hawai‘i.

This psychedelic tourist trap is a leisurely descent into madness.

The tunnel's elegant proportions keep you snug with no claustrophobia freak-out.

Hamburgers are intensely proud of their tunnel beneath the river.

This colorful creation wasn't always a welcome part of Toronto's Moccasin Trail Park.

In Hong Kong, a fairytale flower tunnel is hidden within the gardens of a public housing complex.

A repurposed railway tunnel with otherworldly acoustic characteristics.

The U.K.'s first underground railway line is now a lively thoroughfare for runners and cyclists.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

This former train tunnel is filled with lines from a poem crafted by Robert Louis Stevenson.

Once a sewer culvert, this road tunnel now offers cyclists and pedestrians a subterranean stroll under the C&O Canal.

An abandoned railroad tunnel transformed into a creepy path for hikers and cyclists.

This nondescript tunnel has been featured in a number of iconic movies, from “Roger Rabbit” to “Back to the Future.”

What if the cure for all that ails you was as simple as repeated exposure to low-dose radon?

What began as a prominent Burning Man art piece is now an iconic symbol of downtown Reno.

Monty Python fans will recognize this abandoned mine as the Cave of the Killer Rabbit of Caerbannog.

The Roman Emperor's lost summer home and grotto full of enormous sculptures sit along the Italian seashore.

Generations have refused to move this doll from its dusty resting place to preserve a castle from a watery fate.

Enormous crabs, bioluminescent jellies, and other amazing creatures from the ocean’s depths—some of which are in an aquarium for the first time ever.

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

This chestnut box will not be opened until the country music legend's 100th birthday in 2046.

Hidden behind a wall, Spanish nuns distribute their signature sweets on a revolving tray.

The most remote tree in the world is more than 170 miles from its nearest neighbor.