The Drwęca winds through Brodnica beneath the castle ruins and is the reason the Teutonic Knights chose to fortify the place. It is one of the great canoeing rivers of Poland — slow but never sluggish, lined with reed beds, alder and old riparian forest, and clean enough to support sea trout and otters.
Multi-day kayak trips run from up near Ostróda all the way to the Vistula, often broken at Brodnica for an afternoon in town. Even if you only walk along the bank below the castle for half an hour, you get a good sense of why the river is the spine of this whole landscape.