Located in the thermoelectric factory that once powered the entire city, this Portuguese museum is shockingly fascinating.

A massive 1830s industrial site once known as Czechia's "Iron Heart" has been transformed into a playground of science, technology, and art.

This network of conjoined cellars was riddled with traps and supposedly allowed the townspeople to pretend their homes were deserted.

The world's greatest slide descends 18 stories from this looping mountaintop viewing platform.

Thirty creepy ghosts now inhabit this decaying 14th-century church.

A Jenga-style cylindrical tower of books that appears to go on forever.

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

After being destroyed by IRA sympathizers, the ruins of this stately Irish manor have sat vacant for decades.

A tiny microvalley etched into the side of Knocknarea Mountain hides another world.

This floating garden in the sky is straight out of a fairy tale, but the real thing is nothing short of magical.

One of the most popular megalithic sites in Ireland stands as a humbler version of Stonehenge.

Once the longest bridge in Ireland, this rusting span sits abandoned and overrun by nature.

A giant concrete orb in far north Iceland marks the ever-shifting boundary.

This wrecked airplane has been sitting on a black sand beach since the 1970s.

A winding, blood-red tunnel of hardened lava navigable by foot.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

Architectureal fantasy quarter of Rome.

Plenty of old carney magic still haunts this photogenic amusement park.