We were in Potsdam in the early 1990s, and went around Sanssouci gardens, then noticed what looked like some ruins on a hill the distance. As we approached, there were all sorts of tumbledown classical structures and a huge circular concrete construction full of stagnant water.
Turns out we had stumbled on Ruinenberg where in the mid 18th Century Frederick the Great of Prussia had had a massive water tank built to supply the planned water features of Sanssouci. He surrounded this with artificial ruins, follies, for fun.
Turns out the water tank never succeeded in supplying the water for the gardens, so the fountains weren’t created then. However, around a century later, a pump room was created with the technology of the time, so Sanssouci could have its fountains.
I’ve hunted high and low for the classical follies but cant find the images, so here’s a stagnant pond with a bit of a folly:
Linked to February Squares at Becky’s here