The first tunnel to be dug beneath a river, repurposed as an art and museum space.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

The massive white mound and accompanying water terraces are a striking geological oddity.

An explosion of natural color known as "the river that ran away from paradise."

The mysterious, fantastical woodland inspiration for "The Lord of the Rings."

An exquisite tunnel of cascading flowers.

The sound of swaying stalks in this stunning grove has been named a governmentally recognized sound.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

A once-thriving hotel in the Swiss Alps couldn't compete with climate change.

The randomness of this wall of lava lamps helps encrypt up to 10 percent of the internet.

Science fiction's grandfather has a fittingly marvelous tomb.

An abandoned set from the 1980 film "Popeye," claimed and repurposed as a theme park by creative locals.

This quaint Italian town keeps losing ground as the sides of its plateau slowly erode.

An abused and forgotten metropolis, abandoned for centuries.

This domed temple was built in a hidden cave mouth as a refuge for sinners seeking absolution.

An enormous concrete structure built over a nuclear crater.

Because sometimes the most efficient route from A to B isn't a straight line.

A sculpture of a giant hand reaches for the stars in the middle of the Atacama desert.

Installed at a chaotic intersection, this gave London traffic cops a place to hang their heavy woolen coats.

Giant sand sculptures of famous people and places are on display near the Tottori sand dunes.

An enigmatic modern marker left next to a historic Roman site.

A whimsical sensor instrument for Minneapolitans to play on their walks to work.