Thanks, everyone, for the good ideas! As I said, I don't have a lot of time but will still have at least 4-6 hours to kill on Friday so surely I can do something. I won't have a car but will look into bus routes. And for the nearby stuff, a cab shouldn't be that much (for example, the Winchester Mystery House is supposedly about four miles from where I'm staying; terenz, I'll look up the museum you mentioned).

And Jassy, I'll certainly be at the tech museum -- in fact, the reason I'm going is to attend the Association of Science-Technology Centers annual meeting! And Jerry, that's a good tip. Here in Northern Virigina I've done the same. Just a couple of weeks ago I went to a Potomac Cannons (minor league games) and it's about the same as what you describe.