Lake Wilderness Park is Maple Valley's 117-acre city park on the north shore of Lake Wilderness, and its swim beach is one of the few in south King County that still has lifeguards. The beach is a curve of sand below the lawn with a big L-shaped dock wrapping around the roped swim area, a bathhouse and a concession stand beside it, and the city's Lake Wilderness Lodge on the rise above. Lifeguards are on duty daily from late June to late August, noon to 7 p.m., with a couple of bonus weekend days at the end of the season; outside those hours the beach is open but unguarded, and the city can close it for weather or water quality. During guard season the same stand rents canoes, paddleboards and pedal boats.

The park is free and open year round from 7 a.m. to dusk. There is no motor traffic on the water: internal-combustion engines are banned on the lake, so the launch at the park is for electric motors, paddle craft and rowboats. The lake is stocked with trout, and the annual fishing derby on opening day in late April fills the dock. King County posts bacteria and temperature readings for the beach on its swim beach page.

The rest of the park is set up for a full day. A large playground rebuilt in 2018 has a rope climbing structure, slides, a merry-go-round and an accessible swing; there are three covered shelters and five picnic sites that reserve May through September, tennis and pickleball courts, Patrick's Field for softball, and dozens of picnic tables across the lawn. Dogs are allowed on leash. Alcohol is prohibited. The Green to Cedar Rivers Trail runs through the park and connects to the Cedar River Trail, so it is reachable by bike from Renton without touching a highway.

The 40-acre Lake Wilderness Arboretum, run by a volunteer foundation since 1965, is on the west side of the park and holds one of the world's largest collections of western azalea along with native plant gardens and forest trails. The lodge, a 1950s resort building the city rents for weddings, looks over the lake from all three floors.

The park was a King County park until Maple Valley incorporated and took it over in 2003. Maple Valley Days in June, the Fourth of July fireworks and summer concerts all happen here, and the parking lot becomes a carnival midway for the June festival. The entrance is at 22500 SE 248th Street, off Witte Road, about 30 miles southeast of Seattle.