Bergpark Wilhelmshöhe

Listen for a moment. Under the birdsong and the wind in the beech trees, there is often the sound of water moving over stone. The paths here are gravel and packed earth, and they climb. They keep climbing. Far above you, on the crest of the hill, a giant copper figure stands against the sky, small with distance but impossible to miss. Welcome to Bergpark Wilhelmshöhe, the mountain park on the western edge of Kassel.

This is not a garden in the usual sense. It is a whole hillside shaped into a single idea. A long axis runs from the summit down to a palace at the foot of the slope, and almost everything you see is arranged around it. Over several generations, the rulers of Hesse-Kassel turned this forest into a stage for power, water and taste. In 2013, UNESCO added the park to its World Heritage list.

The story begins around 1700 with Landgrave Karl. A landgrave was a German prince who ruled a territory, and Karl had big ambitions. He had travelled in Italy and seen the great hillside gardens near Rome. He brought back an Italian architect, Giovanni Francesco Guerniero, to design something on that scale for Kassel. The result was the octagon on the hilltop and the long stone cascades below it.

Now look up at the figure on the very top. That is Hercules, the hero of Greek myth, resting on his club after his labours. He is based on a famous ancient statue known as the Farnese Hercules. Here is the first thing most visitors miss — he is not cast or carved. He was hammered together from sheets of copper by a goldsmith from Augsburg, and he was finished in the early eighteenth century.

The octagon beneath him is built of rough volcanic tuff, a porous stone that looks almost like dark sponge up close. It was meant to look powerful and slightly wild, like a giant's fortress. A stone pyramid rises from its roof, and Hercules stands on the pyramid. Together they form the high point of the whole axis. From the town far below, the monument reads as one sharp shape on the skyline.

But the real purpose of all this stone was water. Karl wanted water to fall from the summit all the way down the hill. And here is the second surprise. The whole system still works without pumps. Reservoirs in the hills above collect the water, and gravity does the rest. Pipes and channels from the early eighteenth century and later still carry it down the slope.

On certain days in the summer season, the park runs its water features, and people follow the flow on foot. The water bursts from the octagon and pours down the cascades in white steps. Then it disappears into the woods and reappears at a waterfall, at a stone bridge called the Devil's Bridge, and at a crumbling aqueduct. That aqueduct was built as a ruin on purpose. It never carried anything to a town.

That fake ruin tells you how taste changed. By the later eighteenth century, the strict Italian geometry of Karl's age had gone out of fashion. The new ideal was the English landscape garden — curving paths, lakes that look natural, carefully placed ruins and sudden views. Later landgraves reshaped the lower slopes in this romantic style. So as you walk downhill, you are walking from one century's idea of beauty into another's.

The journey of the water ends at the Great Fountain, in a pond near the palace. Here the pressure built up on the way down pushes a single jet high into the air. When it rises, the crowd usually goes quiet for a second, and then people start cheering. On a sunny afternoon you may see a rainbow in the spray. It is a simple trick of physics, planned centuries ago.

The palace itself, Schloss Wilhelmshöhe, is a pale classical building from the late eighteenth century, built under Landgrave Wilhelm the Ninth. Today it holds a gallery of Old Master paintings, including a celebrated group of works by Rembrandt. The palace has also seen strange guests. Napoleon's brother Jérôme lived here as king of a short-lived state called Westphalia. Much later, in 1870, the French emperor Napoleon the Third was held here as a prisoner of war.

Tucked into the woods on the southern side of the park is another surprise — the Löwenburg, or Lion Castle. With its towers, battlements and broken walls, it looks like a medieval fortress. In fact it was built around 1800 as a romantic fantasy, deliberately designed to look old and partly ruined. It even has its own chapel. It shows how the rulers of Hesse liked to imagine a heroic past they could step into.

Away from the monuments, the park belongs to ordinary life. Kassel families come here to walk dogs, push prams uphill and picnic on the lawns. Runners use the steep paths for training. In autumn, the beeches turn copper and gold, almost the same colour as Hercules. In winter, mist can hide the summit completely. Each season gives the hill a different character, and locals tend to have a favourite path of their own.

Before you move on, find a spot where you can see along the axis. Look up toward the octagon, then down toward the palace and the city beyond. Everything between those two points was planned by people who never saw it finished. Notice the sound of the water, the smell of damp stone and leaves, the feel of the gravel under your shoes. Then take your time on the way down. The hill was designed to be walked slowly.