King Frederick William III of Prussia bought a piece of land bordering the southern edge of Sanssouci Park and gave it to his son and his son's wife Elisabeth Ludovika of Bavaria for Christmas in 1825. There was already a farmhouse on the site. The young couple did not knock it down. Instead, the artistically inclined crown prince — who had ideas of his own and sketched extensively — handed Karl Friedrich Schinkel, the great architect of Prussian neoclassicism, a brief: build me an Italian villa on top of this farmhouse. Schinkel obliged. With his student Ludwig Persius doing much of the practical work, he raised low pavilion walls on the old foundations between 1826 and 1829. The result is small, almost modest by royal standards, and structured like a Roman country house — wings opening onto loggias, a porch shaded by columns, a pool in front. The cost was kept deliberately low. The atmosphere was kept deliberately Mediterranean.

The interior of the ten rooms remains largely as it was. Most of the furniture was designed by Schinkel himself, and what is striking is how unfussy it is — graceful chairs, simple tables, a quiet aristocratic restraint that feels closer to a country gentleman's house than to a Hohenzollern palace. The most famous room is the tent room. Patterned after the campaign tent of a Roman caesar, ceiling and walls are draped in blue-and-white striped wallpaper; window treatments, bed canopy and coverings carry the same striping, so that lying down feels like sleeping under canvas while still in a stone building. The room was used as a bedroom for guests and companions. Between 1835 and 1840, the explorer Alexander von Humboldt — by then in his sixties, the most famous scientist in Europe — was a regular summer visitor, sleeping in the tent. The blue-and-white scheme runs through the rest of the palace too, on shutters and trim, said to acknowledge the Bavarian heritage of the crown princess Elisabeth.

The site was originally flat and partly marshy, the kind of land that does not become a garden by itself. Peter Joseph Lenné was given the job of designing the grounds, and he is the second great name attached to Charlottenhof. Lenné was the most influential landscape architect in 19th-century Prussia, and what he produced here is an English garden — irregular, naturalistic, with mature trees and broad lawns and reflective water features that seem to have always been there. Crucially, Lenné connected the new park visually and physically to the older Sanssouci grounds laid out under Frederick the Great. Walking from one to the other today, the joins are all but invisible, which is the point. The landscape lets Schinkel's small Italian villa feel like one well-placed building inside a much older composition. Officially the place was named Charlottenhof in honour of Maria Charlotte von Gentzkow, who had owned the property from 1790 to 1794 — the kind of acknowledgment of a previous owner that royal estates do not usually bother with.

Since 1990 Charlottenhof has been part of the UNESCO World Heritage Site Palaces and Parks of Potsdam and Berlin, the largest single ensemble of royal landscape in Germany. It is run, like most of these properties, by the Prussian Palaces and Gardens Foundation Berlin-Brandenburg. Visitors who make the short walk from Sanssouci Palace south through the grounds find a building that is easy to underestimate. There is no monumental staircase, no gilded throne room, no fortified wall. There is a Roman pool, a colonnaded porch, and a small handful of rooms in which a future king of Prussia tried, for a few years, to be something other than a future king of Prussia. The Siam House architect grew up to become Frederick William IV in 1840. He commissioned bigger projects after that. None of them feel as personal as this one.