Nürnberg was one of Germany’s — in fact Europe’s — leading cities 500 years ago, with an imposing Imperial Castle. The city’s formidable walls were state of the art — they were redesigned from square towers, which worked just fine before the threat of cannon fire, to round ones — so enemy cannon balls were more likely to glance off without doing any damage.

Back then, with 80 water wheels powering mills along its now sleepy river, Nürnberg was an industrial marvel. The scenic remnants of its hard medieval past are now just an added dimension of a delightfully people-friendly historic center.

Ninety percent of downtown Nürnberg was destroyed in 1945. To rebuild, city fathers had a choice: go entirely modern like Frankfurt did — that was the Manhattan plan — or, maintain the pre-war footprint and rebuild modern while preserving the traditional character — that was Nürnberg’s choice.

With one of Europe’s largest pedestrian zones, the city of half a million has the charm of a smaller town. Playful street art, a series of bridges with scenic river views, and no traffic noise, make it a joy to experience.

Nürnberg is dominated by its mighty castle. In the Middle Ages, Holy Roman Emperors — Europe’s most powerful rulers — stayed here when in town.

The Holy Roman Emperor ruled much of Europe for over a thousand years. The institution was finally ended by Napoleon in 1806. The emperor ruled a vast realm — it was bigger than today’s Germany — but it was never centralized like France or England. Rather than inheriting his power, he was elected by the top bishops and nobles of the day — they were called “prince electors.” The emperor had to keep on the move, and didn’t have a real capital city. While the emperor claimed supreme authority inherited direct from the emperors of ancient Rome, historians like to joke that the Holy Roman Empire was neither holy, nor Roman, nor an empire.

The most famous of these medieval emperors was Charlemagne — shown here in a painting by Nürnberg artist Albrecht Dürer. Charlemagne — or Charles the Great — was crowned by the pope in the year 800.

When ruling from Nürnberg, the emperor would have received visiting delegations in the castle’s Lower Hall. It’s empty of furniture because the imperial court was mobile. Each city would scramble to suitably furnish its royal quarters before the emperor arrived.

The castle’s 800-year-old church is Romanesque in style, and gives a peek at how structured even medieval society’s top one percent was.

It has a triple-decker design: The lower nobility worshipped from the lower level, the upper nobility worshipped at this level, and the emperor, he worshipped above everybody else — from the balcony.

As effective as the castle fortifications were, there was always an ultra-secure refuge of last resort — the towering keep. And security required more than stony towers.

Any good castle needs a secure water source within its walls. And when your castle sits on a high rock, you need a very deep well. This castle illustrates that in a fun and memorable way.

Even without understanding much of our guide’s German, he made it really clear that this well goes way, way down.