A century-old prison in the heart of Vilnius is now a lively bar, dance club, and artist residency.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

This castle resides in a valley known for immense bloodshed during the Middle Ages.

This former lieutenant governor's home is brimming with curiosities.

In a 345-million-year-old cave that's 200 feet underground, dinner awaits.

For six months of the year, three giant mirrors direct a pool of sunshine onto this otherwise occluded town.

The largest cave in Northern Europe.

A bizarre house filled with an astounding array of collections.

A quirky house created entirely out of glass bottles combines a collector's spirit with an artist's flair.

This cave holds a surprisingly colorful variety of geological oddities.

This mesmerizing medieval monastery-cave complex sits thousands of feet above ground overlooking a valley.

This seaside Italian village doesn't just look Escher-esque, it actually inspired the mind-bending artist.

Its appearance in "Game of Thrones" may spur on the long-awaited restoration of this medieval shipyard.

The cathedral of a controversial, conservative, schismatic sect that declared the Catholic Church heretical and founded its own succession of popes.

The world’s highest ski resort was deserted after an 18,000-year-old glacier melted away.

A barbarous band of serpents guard the bases of these Aztec temples.

One of the most well-preserved temples of ancient Egypt.

In this beloved beach town, a secret seafood haven lies tucked behind a car wash.

This Russian bar-restaurant lies within a three-story underground bathhouse.

Famed for its pie, this eatery has a hidden tunnel that allowed Catholics to secretly walk to church during the Reformation.

Get past the gatekeeper's apartment and enter an elaborate hoax of a restaurant with a Masonic feel.

The world's largest underwater restaurant is submerged off the southern tip of Norway.

This is not only one of the oldest collections in Europe, but also possibly the most beautiful.

This 170-year-old Swiss guesthouse built into the side of a mountain is best accessed by a cable car.