At the northern edge of Sopot, just where the city begins to give way to the Trójmiasto Landscape Park, a small early medieval fortification sits beneath a beech forest. The earthworks — ramparts and a surrounding moat — date from the 10th or 11th century and were part of the Slavic settlement of this stretch of the Baltic coast, long before Sopot existed as a German or Polish town.
The site is modest in scale but atmospheric: the beech canopy is dense enough to feel properly forested, the earthworks are surprisingly well-preserved, and there is almost never anyone else there. It's a fifteen-minute walk north from the main town, accessible on foot along the seafront promenade or through the residential streets behind.