The massive white mound and accompanying water terraces are a striking geological oddity.

Hungarian self-built castle.

The Bourbon royal family had this unique octagonal hunting "cottage" built on a tiny islet in Lake Fusaro.

Where Venice's gondolas go for a tune-up.

Gorgeous views of Italian mountains and valleys form the backdrop of this unique open-air theater.

Haunting graffiti left by prisoners of the Spanish Inquisition.

One of the highest emergency huts in the world has been waiting almost a century to give imperiled climbers a place to lie down.

The first Russian Orthodox church in the Catholic city of Rome in almost a thousand years.

Sitting beneath an unremarkable residential building is a museum devoted to classic Pinball.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

Naturally preserved bodies are eerily staged throughout the crypt in varying poses.

This outsider art house has gone from clinical creation to astounding artwork.

Resting in the middle of an Austrian river, this sci-fi "island" lets people cross in neon style.

Double spiral staircases are not unheard of, but they are very rare.

Visitors dip into a variety of pools of what was once ice.

A centuries old castle atop a dormant volcano houses museums devoted to both women and witches.

Each year melting snow turns these Austrian hiking trails into scuba zones.

Trick water gardens from 1619 featuring a 200 piece mechanical theater powered by water.

What looks like a link in Gondor's early warning system is actually a centuries-old Italian fortress.

Beautiful views and Roman-style statues on the Italian coast.

142 ceramic steps become a mosaic once a year.

The forbidden island of the Tuscan Archipelago may still contain buried treasure.

Overlooked amid the tourist bustle of Florence, this museum is dedicated to the craft of stone inlay.

The mountaintop inspiration for Umberto Eco's "The Name of the Rose."