The Exploratorium is huge. Kids (ages 11 and 10) spent all day here, and wanted to hang out longer. There are lockers available for fifty cents (bring quarters) if you don't want to lug your heavy bags around all day. All the exhibits are interactive and well thought out, and there are a LOT of them. Most of them are located indoors in the two story building, though there are some outside as well.
The cafeteria is expensive, but we thought the food quality was good. Disappointing gift shops, the kids were looking for hoodies and shirts, but there really wasn't much of a selection.