Inland Lake is the easy outdoor day from Powell River: close enough for an afternoon, but far enough into the forest to feel like a proper break from town. The park has swimming, canoeing, fishing, and simple campsites, with the lake set among second-growth forest and low hills.
The reason to come even if you are not camping is the 13 km loop around the water. It is unusually accessible for a lake trail, with a gentle grade, boardwalk sections, and shelters along the way. Bring a picnic and make it a slow circuit rather than a workout.