William R. Mason Regional Park is one of the larger green spaces in Irvine, covering 346 acres of grass, trees, and a central lake. In a city where most of the open space is decorative — the ornamental medians and village greens that are part of Irvine's branding — Mason Park is the real thing: a place where people actually go to spend an afternoon, walk a dog, have a picnic, or just sit somewhere that isn't a parking lot.
The lake allows catch-and-release fishing and model boat sailing. Trails loop around the park and along the water's edge. The tree canopy is mature enough to provide real shade, which matters a great deal from May through October. There are picnic areas, playgrounds, and a modest waterfall feature. It's not wilderness, and it doesn't pretend to be — but it does the job of being a functional urban park very well. On weekends it fills up with families; weekday mornings it's quiet enough to feel restorative. Parking is paid but inexpensive. The park sits close to the UCI campus, making it easy to combine both into a half-day on foot.