This small museum tucked within a subway station holds pieces from Madrid's past.

An ancient Egyptian temple in the middle of Madrid, Spain.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

The Swedish flag over this small naval fort signals that the nation is at peace.

A king's bloodstained shirt is among the gruesome collection of artifacts displayed below Stockholm's Royal Palace.

When this 18th-century observatory's meridian was moved, it set Sweden's time back by 0.04 seconds.

This grisly exhibit houses skeletons and weapons from a devastating 14th-century clash.

The discovery of an old wall led to the creation of this fascinating museum about the city in the Middle Ages.

Now a hotel, this former bank was the site of a robbery that spawned a psychological phenomenon.

It is said that each of the white stones in the red facade of this medieval house represents the head of a murdered Swedish noble.

Sweden's "good old days" painstakingly re-created in a model village.

A rare surviving Victorian greenhouse designed specifically to house giant water lilies.

Sweden's first nuclear reactor, R1, can be visited 25 meters underground.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

An illuminated manuscript comprising the life's work of a lone monk, inexplicably decorated with a portrait of Satan himself.

Some of the greatest minds in the history of Hungarian art and science converged in this café.

A museum in the childhood house of a medical pioneer.

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

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

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

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

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

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

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