Croatia's towering concrete blossom grows from the site of a World War II concentration camp.

A tower marking the spot where Yugoslavia began its resistance against the invading Nazis stands neglected, but not quite forgotten.

This stunning, out-of-the-way Croatian monument commemorates a community's uprising against occupying fascist forces.

This Croatian fairytale castle is slowly falling apart thanks to years of neglect.

This beautiful Croatian fortress is haunted by legends of forbidden love.

This modern, multimedia museum takes visitors on an evolutionary journey back in time.

This huge metal monument is slowly being stripped to its concrete skeleton.

Once a state-of-the-art tuberculosis treatment spa, these ruins are now ruled by paintball players.

This scale model of our solar system hid in plain sight for years before a physics team sought out all the planets.

Where the lovelorn find a home for their sentimental keepsakes.

A World War II evacuation tunnel turned into a history display of Croatian state and people.

This 135-year-old weather station studied the effects of the climate on human health.

An elevator into the Baltic Sea.

The first (but not only) upside-down house in Germany.

The NASA scientists behind Apollo 11 started out developing Nazi weapons at this abandoned German rocket factory.

This 1960's Soviet submarine in Peenemünde Harbor claims to be the largest submarine museum in the world.

Hitler's bleak vision of relaxation still stands as a mostly abandoned 10,000-room resort complex.

A long spiraling walkway winds through the woods, and around a copper beech tree at the center.

A steam powered train that runs on city streets.

The world's first and only three-segment bascule bridge folds up into the shape of a capital "N" to let boat traffic through.

A tiny island is connected to the mainland by a private railway that residents travel in their own personal wagons.

WWII rocket launchpad in rural Germany and site of operation backfire.

Home to the world's oldest functioning orrery.

The Suurhusen church tower in Germany leans over farther than the famous Leaning Tower of Pisa.