An underground city of salt.

Countless stories attempt to explain Poland's mysterious J-shaped trees.

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

Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.

The abandoned "Red Star Train Graveyard" is the final rusting place for precious artifacts of train history.

The only natural cave bath in all of Europe.

Hungarian self-built castle.

The abandoned military base looks like a post-apocalyptic wasteland.

One of the largest barracks of the Austro-Hungarian monarchy's military is now an abandoned ruin.

A random tree outside a Budapest hotel has become a DIY shrine to the late singer.

A Trabant car, a kangaroo statue, and a plethora of plants take over this abandoned-factory-turned-bar.

This off-beat, quirky communism-themed bar isn't afraid to poke fun at its history.

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

Museum dedicated to the terror regimes of Hungary.

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

This Budapest bar allows drinkers to leave their mark on the walls, floor, and even ceiling.

These abundant, over-the-top monuments are so widely scattered that they define the entire compact capital cityscape, often leading to jokes about whether there are more statues than residents.

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

Museum celebrating the ocean, with the largest wunderkammer dedicated to sea exploration.

Overshadowed by other, more famous Maltese catacombs, this ancient burial chamber has one of the best examples of a ritual agape table.

Burial grounds for more than 1,000 bodies deep under the modern town of Rabat.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

This tri-part waterfall is a little bit of fairytale beauty in the heart of Luxembourg's Little Switzerland.