This massive stone and steel monument remembers a century-old battle that cost thousands of lives and nearly destroyed the city.

A mysterious tunnel hidden in the shadows of a colorful, historic sanctuary.

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

A gigantic statue of a Russian soldier watches over the ancient city of Plovdiv, a prominent reminder of the Soviet period in Bulgaria.

"Unity, Creativity, Beauty."

Mysterious standing stone formations looks like a petrified forest.

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

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

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

The second-largest Jewish temple in Bulgaria was deserted after World War II, seized by the communist government and then abandoned again.

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

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

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

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

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

An abandoned saucer-shaped monument in the Bulgarian mountains.

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

An abandoned cable car station located on the Danube stands like a haunted house above the river.

One of the biggest Buddhist stupas in Europe, hidden from most locals.

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

One of the largest barracks of the Austro-Hungarian monarchy's military is now an abandoned ruin.

A two-way chairlift system between Zugliget and the highest point in the city.

The abandoned "Red Star Train Graveyard" is the final rusting place for precious artifacts of train history.

Museum dedicated to the terror regimes of Hungary.