One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

Roman ruins top white travertine terraces formed by ancient hot springs.

Monasteries on rock pillars, once accessible only by frayed ropes.

A spectacular cave and a beguiling lake.

This series of Baroque passageways in Vienna's cultural center mix old architecture with modern art.

The world's largest reflecting pool is just two centimeters deep.

Old batteries and frog skeletons reside in this lakeside monument to Alessandro Volta.

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

Pilgrimage site for star-crossed lovers.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

This lurid German fountain plots the sad course of marriage from dating to death.

This 600-year-old home seems to defy physics.

The last bastion of Roman presence north of the Alps looms over a German town.

When a medieval fire claimed the original St. Stephen’s Cathedral, it sparked a pattern of unquenchable organ building.

This Dresden church was purposely rebuilt Protestant after being demolished in World War II.

The oldest Jewish cemetery in Europe survived Hitler's Germany.

It houses the remains of a 17th-century version of the Titanic.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

Giant topiary dog once played a role in a terrorist bomb plot.

The oldest Roman lighthouse still in use.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

The design of this beautifully crafted building was inspired by Norwegian glaciers.