Legends surround an ancient tree trunk riddled with nails for good luck.

Op-art architecture designed for happiness.

The beautiful baroque library of the Hapsburg empire.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

A small marionette collection located within the dark cellars of an 11th-century Austrian castle.

In the middle of a Vienna square, Roman ruins dating back some 2,000 years are on display.

An impressive monument to Poland's independence.

An abandoned football stadium with a tragic past.

A haunting contrast of trains that both saved and took the lives of Jewish children in Nazi Germany.

An imperial church bombed to ruins during WWII now stands as a jagged memorial.

Metro station with a claim to rock n' roll fame.

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

Once the tallest building in the world, this abandoned church is now a monument to the destruction of WWII.

Hidden in plain sight on a gable between two towers on the roof of shipping firm F. Laeisz' headquarter in Hamburg sits an unexpected bronze sculpture.

A symbol for the opposition to nuclear power around the world.

This aged paving stone, marked by a maiden's foot imprint and the tales of her plunge from the cathedral tower, serves as a memorial to a tragic local legend.

After funding was cut for a memorial to the Danish author, the sculptor had his statue ceremonially lowered into the city harbor.

After attracting attention for nearly three decades while standing in front of a church, this phallic stone sculpture is now tucked away in a campus backyard.

This sublime architectural marvel is a rare example of an expressionist church.

The final resting place of one of the brightest physicists of the 20th century.

Once a meeting point for great thinkers, and the midpoint of the country.

The house where a Danish physicist discovered the connection between electricity and magnetism.

One of Scandinavia's largest mosaics pays tribute to Danish art and science luminaries.

This pair of gilded girls atop an Art Deco building in Copenhagen were built to function as a weather indicator.