The romantic botanic tunnel feels like a well-kept secret.

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.

Home to the longest wooden escalators in the world.

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.”

The oldest residential street in Europe also features an optical illusion.

When in Idaho, sleep in a giant potato.

Eyam took steps to quarantine themselves and keep the plague from spreading.

These slanted cubic abodes are a creative if odd solution to a zoning pickle.

This award-winning men's bathroom was just too beautiful to not allow women to see.

After 800 years, Europe's oldest elm tree has met its end.

An Aztec temple, the largest man-made pyramid in the world, sits buried in earth with a Spanish church set on top.

The world's largest bioluminescent area was undiscovered by science until 2005.

Tubing through a cave lit with glowworms is a magical underground experience.

These millipedes glow not out of attraction, but as a not-too-subtle warning.

Australian Lake set aglow by Noctiluca Scintillans.

Bioluminescent firefly squid light up this Japanese fishing port.

Malaysian fireflies create a dazzling display as thousands light up in unison.

Millions of glowing microscopic organisms light up the waters of this luminous lagoon.

These eerie outliers of the lightning bug family glow a mysterious blue color.