If you are feeling athletic, you can rent a bike on Fisherman’s Warf for a small hourly fee, cross the Golden Gate Bridge, and take the ferry back from Sausalito.
Of course, three quarters of the way to the bridge, as the grade steepened, I felt like I was going to die and had to pull over to the side and rest for a few minutes. Some young punk kids breezed past me, casting concerned glances as they asked “Are you ok?” I made it to the other side, felt very refreshed, and had an overall excellent day.