Tucked in the back of Modjeska Canyon, the Tucker Wildlife Center is a great place to spend an hour or a day. The center itself has a Nature Center centered around children's exploration of wildlife, picnic tables under the canopy of a massive oak tree, meandering paved interpretive trails that explore different ecosystems and wildlife, a pond stocked with turtles and fish, an enclosed bird-watching porch with well-stocked feeders for the local resident birds, an open-air amphitheater, and a large variety of both locally resident wildlife and cared-for larger wildlife (think zoo). There are benches throughout. The majority of the area is well-shaded, but some of the ecosystems are full sun.
If you want more adventure, you can continue up the canyon beyond the gate and hike some of the reasonably easy, well-marked wilderness trails, or even strike out on your own up the creekbed and explore remnants of the original water system. (Note: as I found out the hard way, do NOT go up the creekbed if rain is in the forecast, especially immediately after a wildfire. You will get chased out by an avalanche of mud).
For an intense, all-day hike that takes you to a couple of perennial natural springs, go across the street from Tucker's main entrance to the Harding Truck Trail trailhead. The springs are about five-plus miles in, and the trail is entirely uphill and completely exposed (until you get to the springs, where the water allows for a lushness of vegetation reminiscent of a rainforest). The views along the trail get better as you go farther, allowing clear views of the Catalina Islands. There is a picnic bench a little over a mile in -- a great spot to stop for a break. A neat little side-trip on your way up will take you to a waterfall, dry in the summer but usually with a few small pools and seeps: when you get to a sharp right bend with several large culverts under the roadbed, cut up the small canyon to the left; it only goes about 1/4 mile back.
Tucker Wildlife Sanctuary is a destination place for many local school groups.