Köpenick Palace Island

The castle is located opposite the Köpenick town center with the Köpenick town hall on an island in the Dahme, not far from where it flows into the Spree. The island is connected to the mainland by a bridge over the castle moat. In the immediate vicinity is the Long Bridge, which crosses the Dahme and connects the Köpenick old town as well as the castle island and the castle with the newer districts to the west and northwest and the center of Berlin.
Source: Wikipedia

You can get directly to the front of the castle and into the park on the castle island without paying an entrance fee.

The gate to the castle island. Stroll like the nobility once did. In the small park behind it you can still feel like the ladies in their hoop skirts and the men in their suits and top hats ❣️