This former Nazi castle was built as a school to train what would have been the future of the Third Reich.

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

Two standing giants remain as a tribute to Luxembourg's metallurgical past.

A former ironworks that was the first UNESCO industrial site.

Now overgrown, these anti-tank barriers from World War II are sometimes called "dragon's teeth."

A unique hanging cable-car navigates through Dresden, the oldest suspension railway in the world.

This lakeside bunker complex in Mamerki, Poland, housed the Supreme Military Command of Nazi Germany during World War II.

This Nazi ruin was the site where Hitler was almost blown up by a suitcase bomb.

A collection of items from a way of life that no longer exists.

These natural cliffs look like they are a part of an old castle complex.

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

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

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

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

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

Overlooked amid the tourist bustle of Florence, this museum is dedicated to the craft of stone inlay.

South of Bologna, a limestone grotto with a protruding waterfall and a floor full of cave pearls.

This strange bovine gargoyle is said to have been put in as a passive aggressive form of revenge.

The middle finger of modernity.

An incredible menagerie of more than 3 million taxidermied animals at the oldest science museum in Europe.

The largest and most famous wax anatomical collection anywhere in the world.

This museum is rotten with a century of wax medical deformities.

Leonardo da Vinci was one of many to find inspiration in this unique, rocky landscape in Tuscany.

Explore the quarry where the marble was sourced for Michaelangelo's David.