Benrath Palace is Dusseldorf's most graceful palace excursion: a pink Rococo residence set between formal gardens, ponds, and long park avenues. The complex was designed as a pleasure palace, and it still has that light, theatrical quality.
It is well worth the trip south from the centre, especially if you want architecture and fresh air in the same outing. Allow time for the park as well as the palace museums, because the landscape is a major part of the experience.