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

A mountain pass in Bulgaria's Balkan Mountains was the site of four historic battles.

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

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

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

An abandoned saucer-shaped monument in the Bulgarian mountains.

This statue of a 15th-century Hungarian military and political figure has become known for its resemblance to a particular cartoon knight.

This museum houses a large collection of old motorcycles.

What started as a collection of vintage tractors turned into a museum filled with cars, radios, and other oddities.

Different sections of the Zemun Fortress were built in the 14th and 15th century as a response to the advance of the Ottoman Empire.

This medieval monastery represents an architectural blend of eastern and western European culture.

Beautifully carved tombstones fill this unmarked graveyard, uniquely situated near the village's famous stone wine cellars.

A misnamed well, with a deep dark past.

A well preserved medieval fortress in Vojvodina.

A maze of underground tunnels beneath one of the most beautiful forts in Serbia.

Despite being pillaged and destroyed a number over times down the centuries, this historic church still sort of stands.

A grand Yugoslav memorial to the group of partisans who fought and died resisting western Serbia’s Nazi occupation.

Religious perseverance and cultural coexistence manifest in an architectural gem that multiple wars couldn't topple.

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

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

Structure built from the skulls of vanquished foes.

These temples are among the oldest free-standing stone buildings in the world.

This church is named for one of the most dramatic tales in the early Christian church.

Ancient mysterious ruts carved in the bedrock.