Structure built from the skulls of vanquished foes.

A sinuous path among steep cliffs creates a stunning sight in southwestern Serbia.

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

The largest ice cave in the world is thought to be the entrance to hell according to Austrian legend.

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

Yugoslavia's biggest underground airport lies in ruins.

A miniature train-ride through Slovenia's largest cave system.

This abandoned Slovenian military barracks has become a punky-political art squat.

This community on a small Venetian island has taken to painting their houses in bright neon hues.

Sitting on an Italian hilltop is this surreal fortress built by the mad inventor of electrohomeopathy.

Two very green residential towers cleaning the air in one of Europe's most polluted cities.

These spooky and unusual stone formations create an underworldly landscape.

A breathtaking bridge that crosses a vast gorge over a river's torrents, and has a tale of a devil architect attached.

This crumbling, graffiti-covered mansion sits tantalizingly within reach of the proletariat who frequent a public park.

The oldest steel ship in Iceland has been beached for years and is now a rusting ruin.

This volcanic cave lake is essentially hard proof that Iceland is the most magical place on Earth.

Established in 1638 to battle the Black Death, Hortus Botanicus Amsterdam is a treasure trove of rare flora.

Museum preserving torture methods from the past.

The oldest trees in Northern Germany.

A National Historic Landmark with a scenic clock tower and park filled with deer and peacocks, plus a military museum.

This massive wooden building contains a giant Buddha, healing pillars, and tame deer wandering the grounds.

The decaying ruins of Wales' first asylum for the mentally ill.

This abandoned asylum in Wales might look haunted, but it's still beautiful.

This real life asylum of horrors is now an abandoned ruin that hides the unbreakable code to one patient's insanity.