Federal Way is best known ’round the Sound for its amusement and water park, Wild Waves (36201 Enchanted Pkwy. S., 253/661-8000, www.wildwaves.com [1], $35 adult, $30 child, hours vary, open May–Sept.). This enterprise is a nice summer destination to keep the whole family amused. The water park offers 400 feet of white-water rapids on its Raging River Ride, four giant water slides, a "beach" with artificial five-foot waves for bodysurfing, and scaled-down versions of the adult attractions for the kiddies.
All the water is heated, so don't worry about the weather. The dry side of the park has 16 rides (including a 1906 carousel), bumper boats, a free-flight bird aviary, pony rides, children’s museum, petting zoo, and other attractions.
Links:
[1] http://www.wildwaves.com