Gas Works Park is Seattle at its most odd and likable: a grassy Lake Union park built around the rusting remains of an old coal gasification plant. The machinery is fenced and sculptural now, a reminder that this pretty waterfront was once very industrial.
The hill has one of the best skyline views in the city, with floatplanes, sailboats, and downtown all in the same frame. It is especially good around sunset, or on the Fourth of July if you do not mind crowds.