This Polish cave has housed a dragon, a brothel, and an enduring legend.

Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

Inside the corridors of this flea market, visitors are sure to find some obscure and odd treasures.

An ornate private entrance to the Vienna subway built specifically for the emperor.

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

Apartment complexes built into huge repurposed natural gas tanks.

This cubist Vienna church building looks like some sort of alien stonehenge.

The resting place for anonymous victims of the Danube's dark waters.

An old asylum graveyard that's been abandoned for half a century attracts those seeking a dark thrill.

A former squatter's paradise outside Prague.

The palace window through which Protestant nobles flung two Catholic regents, thus sparking the Thirty Years' War.

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

This artificial cave looks like something out of a fairytale.

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.

The tunnel's elegant proportions keep you snug with no claustrophobia freak-out.

This Prague museum collects brutalist relics and memories from the country's former Soviet rule.

The risqué mixed-media sculptures are supposedly a metaphor for Czech politics.

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

A bust of Franz Kafka spins in pieces, reflecting the writer's inner torment.

Walk through Czech history in Prague's largest graveyard.

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

A Jenga-style cylindrical tower of books that appears to go on forever.