Coit tower.

Coit tower is a semi interesting part of the skyline, its shaped like a fire hose supposedly because the person who wanted it built was a fire bug. Turns out that that rumor is WRONG (see the Wikipedia link), apparently not everything they tell you during the bay cruise is 100% fact. Anyway, you should absolutely not try to drive up there, just park in the neighborhood and walk up the hill if you must. I'm not really such a big fan though, I think you can skip the trip there unless you're really hurting for something to do.