Yosemite
Yosemite is one of the most beautiful places to visit in California. It is famous for its steep cliffs, waterfalls and stunning nature. There is a lot to see and do in Yosemite, so most people go camping. You can visit just for one day, but I recommend focussing on the couple things you want to see. Parking can be difficult, so keep that in mind.
Monterrey
There is a whale watching tour we have gone on in Monterrey, CA which we highly recommend. Whale watching is possible all year round, but only certain whales can be seen during certain times of the year.
San Francisco
There are a lot of things to see and do in San Francisco. I suggest taking the ferry into the city and then taking public transportation around. However you can also drive. Parking can be challenging in some parts.
Sonoma or Napa Valley
There are a lot of vineyards that you can visit that are nearby. Please ensure to have a dedicated driver (BOB).