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

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

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

UNESCO-protected ancient burial ground.

Said to be the only museum in the world dedicated to the most classic of all blooms, the rose.

An abandoned saucer-shaped monument in the Bulgarian mountains.

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

A magnificent, glittering building tucked into a tiny Bulgarian mountain town.

An homage to the medieval rulers of Bulgaria.

A patchwork of ruins from various civilizations in one of the world's oldest continually inhabited cities.

The cave holds a spectacular array of stalactites and stalagmites, including one shaped like a giant human heart.

The oldest arboretum on the Dalmatian coast doubles as the gardens of Kings Landing in "Game of Thrones."

A small and surprising passageway in Saint Petersburg devoted to the Beatles.

This obscene artwork on the side of a newspaper office pokes fun at a rival paper's former editor-in-chief.

A peculiar trapezoidal building covered with wonderful humorous reliefs.

Several of these strange cone-shaped bunkers can still be seen around the former Nazi headquarters.

A wonderfully versatile natural history curio cabinet preserved since the 1840s.

A simple tribute to the microscopic arachnid that gives its juices and its life to help make a speciality German cheese.

A Neolithic celestial calendar standing in a nondescript wheat field.

This neighborhood of futuristic ball houses looks like an alien settlement in a science fiction film.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

This massive collection of taxidermy is full of specimens collected by missionaries during their international travels.

The Netherlands' first car tunnel has an unusually rectangular shape.

A true Valhalla for cactus and succulent lovers.