Vortex-shaped aquarium hosts Europe's largest school of piranhas and other ocean creatures.

This sublime architectural marvel is a rare example of an expressionist church.

A Belgian self-built tower inspired by the Bible and ancient civilizations.

This recently restored crypt was once plagued by liquefying coffins and exploding caskets.

Take a leisurely walk through the park to find the seven giant troll sculptures hidden throughout the park.

The vast chamber inside this abandoned cooling tower looks like something out of a sci-fi dystopia.

Ancient man-made caves underneath small town Belgium.

Part modern art project, part traditional chapel, this see-through church is only substantial from the right angle.

Space-age monument to an early 20th-century uprising.

Abstract monuments express sorrow and resilience at the site of a horrific massacre in Nazi-occupied Serbia.

This fresco-covered medieval monastery hangs from the side of a steep cliff.

This mesmerizing medieval monastery-cave complex sits thousands of feet above ground overlooking a valley.

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

The social hall of this former factory is a Communist-era time capsule.

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

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

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

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

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

This building has two facades of clashing architectural designs.

The temple that withstood the Nazis.

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

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

This tiny Bulgarian town offers a stunning location in the mountains and a storied history.