The only reason why I know about Castro Valley, CA is because I am from the San Francisco, East Bay. Castro Valley is like most smaller towns in the area, it's nice and kind of quiet. It's a great place to live and have some fun but doesn't have a bustling nightlife. This is a great city for families.
Lake Chabot is probably the largest family attraction. It's a great park for having picnics and it even has a theater that features plays throughout the year. Other amenities at Lake Chabot include a tennis court, basketball court, and softball field. I've also enjoyed bowling in Castro Valley in the past.
The San Francisco Bay Area is known for its diverse variety of food. Castro Valley is no exception to this. There are a lot of restaurants and eateries to enjoy. I am a fan of burritos and have frequented the Burrito Shop in Castro Valley. There are different Burrito Shop restaurants in the Bay Area but they all have a slightly different selection and flavor. I like Castro Valley's Burrito Shop.
Castro Valley isn't known for its club scene. You can travel to San Francisco or San Jose for near by clubs. I can't really say Castro Valley has any upscale dining, if you're interested in finer dining selections, you may consider visiting another city near by. Like I said, Castro Valley is most ideal for families.