A Gothic cathedral created from volcanic rocks.

A 14th century bridge built as a fortress, where the devil lurks on one of its towers.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

An impressive collection of over 50,000 minerals including moon rock from the Apollo 17 mission.

This naturally-sourced hot spring is now home to a clothing-optional resort.

Crystal clear lake with a shoreline of travertine located in a Colorado canyon.

This striking public art installation is suspended above a public park, designed to gently move in the breeze.

A Texas cave network is home to some of the world's most spectacular-looking and bizarrely named mineral formations.

360-degree virtual reality chamber physically immerses scientists into their data.

From the sky, a kaleidoscope of color brightens the grey landscape of the San Francisco Bay.

35,000 grape hyacinths flow like water down a garden hill.

A gothic palace of endless stalagmites and pseudoscorpions waits within one of the world's most beautiful caves.

In which a local geological marvel becomes a quaint roadside attraction.

River pirates, murderous bandits, and serial killers used this Illinois cave as their debauched hideout.

This small section of the Sleepy Hollow Cemetery is rotten with famous authors' graves.

A humid oasis combines recreation with exploration in a unique underwater cavern.

This dark, quiet forest on the outskirts of San Diego is dense with rumor and lore.

A cave's rare beauty held a cavernous secret hidden underground.

A mysterious light floating in the trees of Arkansas may be a piezoelectric effect.

A secretive collection featuring objects that were designed specifically for U.S. intelligence operations.

Bizarre Cavern.

Imagine playing a version of Legends of the Hidden Temple, but with a distinctly Southern Gothic flare.

This natural wonder drops 16 stories straight down through rare flora and streaming waterfalls.

Sail through this subterranean show cave that is home to a legend that would go on to name nearly everything around it.