Junipero Serra Park is a 108 acres of trails and other outdoor enjoyments, like two playgrounds and picnic tables. Its hilly location leads you to an impressive view over the Bay right in view of the San Francisco airport. The Meadow View playground is near its highest point. There are some climbing structures, but the two parallel 54-feet metal slides are the focal point of this playground.
Imagine a speedy slide while watching planes land and take off. The playground is in the middle of a woody area and has plenty of shade. Parking is $6 and you can pay right next to the playground. 
I also hiked part of the 1.2 mile Quail Loop Trail which starts next to the playground. On my visit I saw some wildflowers, but not the Douglas Iris that an information sign talked about. Overall it was a pleasant hike with some elevation and a spectacular view!
Junipero Serra Park is just east of 280 at 1801 Crystal Springs Rd, San Bruno, CA 94066. Parking is $6, dogs are allowed on leash.
Are you a slide enthusiast? If so, you should also try the Magic Mountain slide in San Mateo. At 55-feet this is the metal longest slide in Northern California!