If you've never been, and you love museums and/or architecture, this is the one. And, Sunday Oct 8th is the last day of the Keith Haring exhibit. General admission is free (the Haring exibit is not, boo), but make sure to reserve your tickets far in advance as the place "sells out" quick.
For all our out-of-towner's, if you're looking for a gorgeous drive up HWY 1 in your rental car, make Neptune's Net your destination for lunch. Look, it's fried seafood. It's fine. But you're not going for the food. You're going for the drive and the views and maybe an adventure you didn't know you needed.