The spa town of Bad Nauheim is about 20 km north of Frankfurt.
Now this structure needs some explanation: it is a graduation tower, these devices were used to produce salt from the middle ages to the early modern age. Water from springs that contain salt runs down this wooden frame that is stuffed with twigs, mostly brushwood. The water evaporates and leaves a salt crust on the twigs. You find them in some spa towns, mostly in Germany, Poland, Czechia and Austria, because the mineral rich water droplets in the air are said to have the same health benefits as breathing sea air.