I don't really know what you can do for fun, but for food, downtown Mountain View is good (Castro Street). My favorite ramen place (Maru-Ichi) is there, and another good ramen place is Ryowa. There's an excellent gelato place on Castro also; I think it's called Gelato Classico. I forget what else is there (I usually just go for ramen), but Castro St. is like 90% food.
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