Ruins of an early Roman Christian church dating back to the 4th to 5th centuries.

UNESCO-protected ancient burial ground.

An ancient Thracian city where fire rituals were practiced on the largest cult altar in Southeast Europe.

This historic black and white monastery is one of Bulgaria's architectural jewels.

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

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

South Korea's love of the silly photograph is on full display at this goofy collection of trompe l'oeil paintings.

Mirrors and glass shards cover every inch of this arrestingly beautiful mosque.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

A swing to dangle you off the very edge.

A solitary tree has grown up all alone on Lake Wānaka, backdropped by the beautiful Southern Alps.

One of the world's oldest and most massive living organisms is a grove of quaking aspens.

This stunning mass of ice spans 121 square miles and is still growing.

This remarkably well-preserved mosque stands amid an 11th-century caravansary.

Five ancient libraries, little changed for centuries, preserve a medieval archive of Quranic lore and civic documents

It's hard to believe the dizzying patterns covering this abandoned mine are completely natural.

This rare example of a "tidefall" is a spectacular drop from the cliffs down onto the beach.

Twice a day a speeding train passes only inches from the homes of this residential neighborhood.

An abandoned railroad tunnel is now filled with bioluminescent bugs.

A perfectly preserved example of a fortified Medieval ricetto.

The "Versailles of the Jungle" built by a dictator is now a decaying shadow of its hubristic grandeur.

This famed Silk Road oasis was one of the largest cities in the world before it was destroyed by a Mongol horde.