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

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

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

Cold war icon and onetime "hole" in the iron curtain.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

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

The celebrated eyesore created by starry-eyed sweethearts.

An abandoned saucer-shaped monument in the Bulgarian mountains.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

France's most famous cemetery, with some of its most curious tombs.