Topanga State Park is known for its hiking!
If you're feeling really enterprising, there is a $1 bus that travels from Woodland Hills up north, through Topanga Canyon, down to the beaches of Santa Monica, and returns around dinner time. This probably shouldn't be your transportation on the wedding day, but maybe you want to explore while you're in town.
A classic. This is where we ended our 3,000-mile road trip to move Aubrey from New York to LA - it's the "official" end of Route 66. The historic pier still offers carnival rides and games, or you can just walk out to the end and watch the fishermen. Bring a jacket - it gets windy out there!