A hilltop monastery on the Greek island of Hydra.

View the ancient remains of buildings and the ancient "River of Hades" before hopping on a train.

These caves secretly held national treasures during World War II.

Elaborate stone houses constructed from the ruins of war.

This lesser-visited World Heritage site in Athens boasts an impressive ensemble of medieval gold mosaics.

After a catastrophic forest fire, a Greek artist transformed scorched tree trunks outside an old sanatorium into this haunting sculpture garden.

The abandoned summer estate of the former Greek Royal Family.

This former mill comes to life during the Christmas season.

This little-known, 35,000-specimen collection in Greece is a lepidopterist's dream.

A two thousand year old brothel uncovered in Northern Greece.

At almost 900 feet long, this is Bulgaria's longest suspension bridge and the only way to reach the small village of Lisitsite.

In a long-dry lake bed, these groups of massive stone pillars bear a striking resemblance to clumps of everyone's favorite fungi.

This tower is all that remains of the mosque that once stood in the center of the city, before it was destroyed by fire in 1941.

This once-grandiose behemoth of a monument from the socialist era now sits quiet and closed up.

These natural cliffs look like they are a part of an old castle complex.

This massive concrete sculpture is said to be the heaviest communist monument on Earth.

Rock carving created 1,300 years ago 75 feet off the ground.

Crossing a suspension bridge above a forest is the only way to reach this 12th-century monastery.

Mysterious standing stone formations looks like a petrified forest.

Massive, unfinished broadcasting station stands as a monument to the fall of communism.

Housed in a historic 1840 home, this museum provides a window into the lives of everyday, 18th- and 19th-century Bulgarians.

Once an opulent Art Nouveau hotspot, the Constanța Casino is one of Romania's most beautiful abandoned buildings.

An ancient Roman snake god, carved expertly into stone.

The possible imprisonment of Vlad the Impaler here earned the medieval castle its nickname, "Dracula's Castle."