Places I go (or would like to)
I live in San Francisco, so my most-frequented place is Marshall's Beach. (Note: Marshall's Beach is the correct name for what people often mistakenly refer to as "Baker Beach" or "North Baker Beach." Marshall's Beach is the beach that is adjacent to the Golden Gate Bridge. All of Marshall's Beach is clothing-optional. Baker Beach is the state beach that is slightly further south. However, only the north end of Baker Beach is clothing-optional.)
Occasionally, I also take a trip farther south to Panther Beach just north of Santa Cruz. It's a beautiful beach and is never crowded. Bonny Doon is another nice beach down there, but Panther is a little nicer IMHO.
Also occasionally, I go to Kabuki Spa in San Francisco if I want to soak in a hot tub for a while.
One of these days, I'll get up to Harbin Hot Springs. There's also some naturist retreat in the east bay (I forget the name) that I might try. Yes, I know about Lupin, but it's not sufficiently interesting to justify the long drive from SF (I have been there a couple of times).