A striking 12th-century-style castle built on the edge of a cliff.

This old wooden funicular railway leads to a cemetery in the forest.

Remnants of a cone-shaped Nazi bomb shelter.

A German town is growing a building out of trees.

A remarkable two-country morph, this town is part of Germany legally but is by all other measures Swiss.

One of the world's oldest fossil exhibits is on display in a beautiful antique "naturalienkabinett."

The Tübingen University anatomical collection hosts an example of an extremely rare medical phenomenon.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

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

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

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

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

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

One of the largest mines in Bulgaria is now home to a vast museum more than 100 feet underground.

This building has two facades of clashing architectural designs.