In the middle of a Vienna square, Roman ruins dating back some 2,000 years are on display.

Apartment complexes built into huge repurposed natural gas tanks.

A silly medieval mural preserved on the side of a Viennese house.

Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.

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

Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.

The final resting place for the remains of 143 Habsburg royalty.

The beautiful baroque library of the Hapsburg empire.

A unique hotel for the artistic soul.

An artificial hill and apparent calendric structure built in the Early Middle Ages immortalizes a legendary Polish princess.

Inside this Krakow church, an explosion of psychedelic color.

A 90-ton, gravity-defiant steam locomotive shoots for the skies in this bizarrely beautiful public artwork.

A collection of old neon signs from all over Poland line a secluded courtyard.

This walkway is so narrow it needs its own light to stop pedestrian traffic jams.

What looks like a crashed Zeppelin is actually a bright, airy reading room perched atop a modern museum.

This artificial cave looks like something out of a fairytale.

A steampunk-styled three-floor factory churning out art, activism, and electronic beats.

Walk through Czech history in Prague's largest graveyard.

The hidden lair of an alchemist rediscovered in a 2002 flood.

Countless grotesque faces stare out from this eerie Prague art wall.

The history of occult science is turned into a creepshow at this lurid Prague tourist attraction.

Two stunning 17th-century libraries and a cabinet of curiosities.

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

Among the ostentatious rococo ornamentation of this church, an image of death cuts the life-thread.