This ruined castle is said to be the legendary keep of a Viking princess.

Believed to hold the remains of Japan's most infamous fox spirit, this stone is said to kill those who dare approach.

Though they look like Hobbit houses, these semi-underground stone structures were built for winemaking.

An incredibly well-preserved piece of ninth-century Viking poop.

A collection of art from Bulgaria's time as a communist state.

A Roman monument to their own civil engineering prowess.

This 15th-century Serbian Orthodox monastery also contained a school for illuminating manuscripts.

A hidden stream deep in the mountains creates one of the largest tufa waterfalls in Serbia.

The ruins of this medieval castle on a foggy hill tell the story of a once-mighty empire.

The interior of this Serbian royal family's mausoleum is covered with exquisite mosaics.

Ride in 1960s style on the private luxury train Marshal Josip Tito used to travel around Yugoslavia.

A sinuous path among steep cliffs creates a stunning sight in southwestern Serbia.

Structure built from the skulls of vanquished foes.

The remarkably well-preserved final resting place of a powerful ancient Thracian king.

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 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.

Underneath this Byzantinian church lies a necropolis filled with ancient tombs and the ruins of previous churches.

A striking symbol of the Bulgarian capital.

Eastern Bloc nostalgia, anybody?

"Holy Wisdom" overlooks the city that became its namesake.

A Bulgarian monument to Russia's role in World War II is constantly being painted in pop culture protest.