The housing page on the Summer Sessions site has valuable resources for locating summer housing in Berkeley. Students often find it helpful to live within a 15-minute walking radius from campus, but bus service to campus is also robust. Some Berkeley students will post on Facebook to find summer subletters; several groups have names like "UC Berkeley Off-Campus Housing." Beware of scams, and do your due diligence in evaluating a possible housing opportunity.
While living in Berkeley, you will have access not only to a world-class university, but also unique cultural institutions around the Bay Area. Go to the famous Sunday brunch at Wat Mongkolratanaram, or visit Berkeley Bowl and buy vegetables you've never even heard of. Visit the galleries and take in a movie at the Berkeley Art Museum/Pacific Film Archive, just steps from campus. BART will take you to San Francisco or Oakland: visit the de Young or the Legion of Honor Museum and explore Golden Gate Park, or head down to Lake Merritt for a stroll on a sunny day.