Altstadt Köpenick is one of Berlin's more self-contained old-town quarters, set on a small island-like patch of land where rivers and canals tighten around the historic centre. The draw is the mix of water, lanes, Köpenick Palace, and the Neogothic town hall.
It feels different from central Berlin: quieter, older, and more provincial in the best sense. Come for an unhurried walk, then add the palace museum or a waterside meal if you want to make the trip across the city feel worthwhile.