The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

Naturally formed rock city in Poland.

This now-defunct synthetic fuel plant was once a major cog in the Nazi war machine.

Countless stories attempt to explain Poland's mysterious J-shaped trees.

The hidden lair of an alchemist rediscovered in a 2002 flood.

This cavernous swimming spot doubles as a home to the largest known colony of bats in Central Asia.

Ancient catacombs form the foundation for this Rococo orgy of a church.

One of the world’s longest pedestrian suspension bridges.

This gaping hole in the middle of a remote mountain lake looks like a portal to another dimension.

Local lore says the devil built this beautiful medieval bridge to help a fleeing bandit.

This abandoned five-star hotel is now a five-star urban exploration destination.

An abandoned mine now resembles a post-apocalyptic landscape of derelict buildings and blood-red pools of water.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

Houses are tucked between, on, and underneath giant boulders.

Through the colossal entrance to this cave you'll find limestone tubs and an underground waterfall.

The ridged layers that make up this river canyon represent Earth's geological history.

The bizarre rocks of Đavolja Varoš are the result of natural erosion.

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

The possible imprisonment of Vlad the Impaler here earned the medieval castle its nickname, "Dracula's Castle."

A Bulgarian monument to Russia's role in World War II is constantly being painted in pop culture protest.