These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

One of the best-preserved Roman amphitheaters is still used today, but for less brutal events.

The now-overgrown beach resort was once frequented by Yugoslav military elite.

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

The complex has been abandoned since the Croatian War of Independence, barring a stint as a set for 'Game of Thrones.'

This truly palatial work of Communist-era architecture now sits crumbling on a Croatian beach.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

A giant glider—designed by the father of the Rubik's Cube's designer—now soars within a shopping mall.

From cartoon characters to tiny tanks, a guerilla sculptor's little bronze statues are hidden throughout the city of Budapest.

This easily overlooked memorial immortalizes the scars from the 1956 Hungarian Revolution.

A two-way chairlift system between Zugliget and the highest point in the city.

A Trabant car, a kangaroo statue, and a plethora of plants take over this abandoned-factory-turned-bar.

Museum dedicated to the terror regimes of Hungary.

A peculiar clock commemorates a historic victory won by ringing the noonday bell an hour early.

Europe's second largest ossuary wasn't discovered until 2001.

The topiary maze at the Habsburg hunting lodge.

The Habsburgs' royal collections of art and wonders.

Beautiful Austrian natural history museum with carved ceilings and row after row of ancient taxidermy.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

Op-art architecture designed for happiness.

Launched by Napoleon's soldiers more than 200 years ago, a cannonball remains embedded in the tower wall.

The abandoned military base looks like a post-apocalyptic wasteland.

One of the largest barracks of the Austro-Hungarian monarchy's military is now an abandoned ruin.

An abandoned cable car station located on the Danube stands like a haunted house above the river.