As much as I hate having to schlep across San Francisco to get there, the Palace of Fine Arts and its lagoon are among my favorite places in the area. It's just lovely, and has neat history, and I've been visiting it most of my life. I'll be sad when the Exploratorium moves to the waterfront at the Embarcadero, just because fewer people will incidentally be exposed to the Palace of Fine Arts.
Here's a neat video from the air, from a little bitty airship, so you can see how lovely it is.
10 hours ago