If the weather is good, the ferry to Sausalito is nice.
Just go to the Ferry Bldg. at the foot of Market St. You also can buy a book of 10 trips for about $30, it makes sense if you have 5 people with each way needing 1 coupon. The boat takes about 35 minutes each way, if your pressed for time take the same boat back to SF. Otherwise walk around Sausalito and see the galleries, houseboats or a cafe.