A Roman monument to their own civil engineering prowess.

The growing stones of Romania.

Stone pillars and a petrified wedding party in the hills of North Macedonia.

An alien landscape on the banks of the Aegean Sea.

An autonomous republic of Orthodox monks.

This famous city eluded concrete detection until the early 2000's.

Bizarrely shaped rock formations in northwest Bulgaria come with equally bizarre legends.

This tiny Bulgarian town offers a stunning location in the mountains and a storied history.

Mysterious standing stone formations looks like a petrified forest.

A spectacular Bulgarian cave resembling a devil's head with a waterfall rushing down its throat.

The ceiling of Prohodna Cave in northern Bulgaria affords a peek at the sky via two deity-sized-eye-shaped holes.

An architectural marvel that spans the Arda River, and has stories of a haunted past.

The true depths of these stunning Moroccan caves are unknown.

Beautiful carved tunnels.

Large Hadron Collider and the Birthplace of World Wide Web.

While not Turkey's deepest underground city, this subterranean redoubt is the largest.

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

This ancient subterranean megalopolis is known for the hot oil traps that were installed above each of its entrances.

These medieval tunnels provided water to the city above through centuries of civil war and plague.

A waterfall 600 ft. inside a mountain, once the bane of gold miners, is now a spectacle of nature.

Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

This network of conjoined cellars was riddled with traps and supposedly allowed the townspeople to pretend their homes were deserted.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

An abandoned saucer-shaped monument in the Bulgarian mountains.