A unique two-level bridge designed to honor a king.

This unique structure allowed boats to bypass underwater mine barriers in the channel to enter the harbor.

This picturesque medieval monastery guards a small trove of historic treasures.

Humble beginnings for one of the world's most famous scientists.

The complex has been abandoned since the Croatian War of Independence, barring a stint as a set for 'Game of Thrones.'

Where the lovelorn find a home for their sentimental keepsakes.

The big toe of this towering monument to a Croatian national hero is worn from years of superstitious rubbing.

A spectacular Petrine Baroque summer palace commissioned for Catherine I by Peter the Great.

Unfortunately, you can no longer spend a night in this single-person treetop hotel.

This poignant sculpture of a gnarled weapon is a symbol of non-violence.

This giant subway sculpture celebrates the fruit that inspired the theory of gravity.

The world's largest model of our planetary system.

This 135-year-old weather station studied the effects of the climate on human health.

One of the best-preserved Roman amphitheaters is still used today, but for less brutal events.

Now harmless, this looming post struck fear into the heart of medieval troublemakers.

When a supermarket opened up shop within a medieval building it became protected by UNESCO on a technicality.

A full figure 4th century incorruptible saint lies in a glass coffin in Croatia.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

This statue and park honor the Swedish chemist Jacob Berzelius, one of the founders of modern chemistry.

A heated statue pays tribute to one of Sweden's great actresses.

A miniature model of the iconic Stockholm department store.

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

This gem from the industrial age helps visitors and residents alike traverse hilly Stockholm.

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