A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

Even Henry David Thoreau found this glacial pothole irresistible.

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

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

A trough of 700 strange bronze faces runs through a narrow alley in Ljubljana's old town.

Hungarian self-built castle.

The remains of an entire Roman city can be explored in this interactive museum.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

Austria's ultra-modern art museum looks like Cthulhu's giant alien heart.

The world's most important buildings shrunk to a tiny size.

This spire on an Austrian mountain is wrapped around a long spiral slide and has the world's tallest wooden observation deck.

This tiny patch of arid sand sits in one of the greenest states in the United States.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

A six-story treehouse offers spectacular views of New York's Finger Lakes region.