Immerloo Park is a broad green space in Arnhem South, useful if you are staying in that part of the city or want an everyday Dutch park rather than a formal sight. Ponds, paths, lawns, and tree belts make it good for walking, running, or letting children burn off energy.
For visitors based near the centre, Sonsbeek is the more obvious park. Immerloo is quieter and more local, and it works best as a low-key outdoor stop when you are already south of the Rhine.