"Medieval" castle built in the mid-20th century by one family.

The massive white mound and accompanying water terraces are a striking geological oddity.

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

Legions of Roman soldiers bathed in this ancient spa complex under a Budapest transit station.

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

The remains of an entire Roman city can be explored in this interactive museum.

Hungarian self-built castle.

This hidden art nouveau gem was designed by an architect in search of a national style.

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

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

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

A series of caves under Castle Hill that once held the prisoner Vlad Tepes, better known as Count Dracula.

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

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

A 19th century artistocrat's mansion, turned into a library, hidden in a modern library.

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

A small Denmark town displays a pair of titanic jaw bones as their community symbol.

An old Danish political institution where members of government can grab a drink off the record.

Danish observation tower designed to look like a giant beer bottle.

Denmark's famous pseudo-hill.

A little-known cafe in an old copper bridge tower with 360-degree views of the harbor.

A public display of random paleontology.

Bored potato-guarding Nazis etched their thoughts onto a brick storage building in Copenhagen's Meatpacking District.

The decaying remains of a 1960s mechanical wonderland that never officially closed.