Not mentioned above is chinatown, coit tower, and much more.
Two days isn't enough.
If you haven't experienced redwood trees, one of my hidden favorites was
Hoover Redwood Grove
The city is very big for less than 7 miles across. You'll have plenty to do.
Traffic moves very fast and random.
Parking...well...good luck.
To the north is open vineyards and extremely nice coast,
To the south is surfers and hippy small town feeling with redwoods till you reach Monterey,
To the east is the Bay Bridge leading to even more city(don't even attempt except weekend days).