Hungarian self-built castle.

A forgotten graveyard lost in the tangles of an overgrown garden.

This hidden art nouveau gem was designed by an architect in search of a national style.

Tucked away near more famous landmarks lies a statue meant to symbolize the confluence and continuing development of human culture.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

Once the home of a hermetic monk, this cave now houses a small church.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

This Budapest bar allows drinkers to leave their mark on the walls, floor, and even ceiling.

This heart-shaped island looks substantially less lovely after a recent bulldozing project.

This picturesque medieval monastery guards a small trove of historic treasures.

When Croatia became independent of Yugoslavia, the splintering governments left behind these concrete tunnels.

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

Legend has it fairies gathered at the site of this medieval castle.

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

The remains of a sunken military ship wreck visible through clear water.

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

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

Where the lovelorn find a home for their sentimental keepsakes.

The amazing wonder cabinets of a very rich Austrian archbishop.

This 19th century cyclorama acts like an analogue time machine to a different era.

Amidst medieval and baroque buildings, five human-sized gherkins stand tall.

Site of the 1889 murder-suicide of crown prince Rudolf and his lover Mary Vetsera.

Dine amidst exotic plants at this former royal greenhouse.

The world's oldest known salt mine.