A Nesting Doll of Churches.

Pilgrimage site for star-crossed lovers.

Go inside to really appreciate this 500-year-old technological masterpiece.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

The yawning maw of this pagan visage is said to bite off the hands of liars.

The underground sanctuary of a mysterious ancient cult.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

Pompeii's less famous neighbor is still revealing her secrets.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

Once the home of a hermetic monk, this cave now houses a small church.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

Take a walk in a recreation of ancient Rome.

Cold war icon and onetime "hole" in the iron curtain.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

Macabre astrological automaton clock dating to the late 1400s.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

A turn of the century building boasting some of the most beautiful art nouveau architecture in Prague.

The slender brass strip in Prague's Old Town Square was used to tell time from 1652 to 1918.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.