While in SF: Don't miss the Alcatraz tour...get your tickets early. Tour the WWII submarine USS Pampanito, which is permanently docked at Pier 45. Try riding the Cable Cars too...the POWELL-HYDE line has the best views and the CALIFORNIA line is the least crowded. The Cable Car Museum is really interesting too. Head up to Twin Peaks for a fantastic 360° view of the City.
Here's some info on hiking around the SF Bay Area:
https://www.timeout.com/san-francisco/things-to-do/best-hikes-in-san-francisco
Driving around SF is a total PITA and trying to park a car in the downtown area is nearly impossible...use public transit if you can. And bring some warm clothes...Spring weather in SF can still be quite chilly, especially in the evenings.
The Blackhawk Museum across the Bay in Danville is worth a visit if you want to see some amazing classic & vintage sports cars showcased in a beautiful purpose-built facility.
If you make it down to Carmel, be sure to visit the Monterey Bay Aquarium right next door on Monterey's Cannery Row.