A small etching on the white marble parapet was written in runic script by a Viking mercenary.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

A marvel of Byzantine engineering under the streets of Istanbul.

This building has two facades of clashing architectural designs.

The Grand Mall in Varna hosts one of the biggest collections of Soviet-era paraphernalia in Bulgaria.

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

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

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

Outstanding, eerie frescoes and decorations fill this 19th-century monastery.

Mysterious standing stone formations looks like a petrified forest.

This ancient theater, restored in the 20th century, lives on as a venue for dramatic and musical performances.

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

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

The site of many battles and tragedies, including the 40 maidens who leapt into the sea.

A flamboyant five-story building in Bulgaria resembles a crawling snail.

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

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

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

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

This castle played host to the largest great hall found in medieval Central Europe.

For decades, Hungary's Communist Party insisted this gulag had never existed.

Inside the Šomoška National Nature Reserve exists a unique rock formation rarely seen in the world.

The massive white mound and accompanying water terraces are a striking geological oddity.

This Hungarian stilt village is built in a lake that never freezes over due to the power plant that that uses it as a cooling pond.