Op-art architecture designed for happiness.

An 18th century fountain and two columns are all that remains of Rome's forgotten river harbor.

A small cell adjacent to this church was once the bedroom for a renowned saint.

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

An Italian hillside ghost town.

People have been living in the cave houses on this Italian hillside since the Neolithic era.

Massive galleon from a box-office bomb docked in Genoa.

Filled with goldfish swimming in a shallow pool of sea water, this ancient crypt is more wishing well than burial site.

A series of playful yellow penguins share a serious message about the environment.

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

Macabre astrological automaton clock dating to the late 1400s.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

Vienna's giant wonder wheel had a starring role in one of the greatest noir movies of all time.

Baroque celebration of the end of the Great Plague of Vienna.

Swarovski's museum/theme park is a fake diamond fantasia overlooked by a giant.

Originally envisioned by King Ludwig II to rival Versailles, Herrenchiemsee's "New Palace" remains half-gilded for lack of funds.

Also known as the Blue Church, the building was consecrated to the daughter of Andrew II.

The largest fountain in Bratislava.

This Slovakian statue of an emerging sewer worker might just be a bronze peeping tom.

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.