Contra Costa County
East of the Oakland Hills that border the East Bay, Contra Costa County maintains a very separate culture and lifestyle than its Bay Area neighbors. The area is mostly residential -- although many San Francisco businesses have moved here to avoid high city taxes -- and affluent, and consequently considerably more conservative (by Bay Area standards). The same hills that keep Contra Costa culturally isolated also keep it protected climatically; the area is usually 10-20 degrees Fahrenheit warmer than the Bay.
Highway 24, through the venerable Caldecott Tunnel, is the main entrance to Contra Costa from SF, Oakland and Berkeley. From the south bay (e.g. San Jose) you can take Interstate 680.
BART serves Orinda, Lafayette, Walnut Creek, Pleasant Hill, Concord, and Pittsburg. BART stations have bus service as well. Paratransit (for disabled riders) in Contra Costa is quite good, but you must sign up for it with County Connection LINK and you must reserve your rides in advance. In general, rush hour/commute times in Contra Costa feature traffic jams on the freeways and crowded BART trains.
Contra Costa has a lot of parks and trails, as well as reservoirs and house museums. Look up the websites for East Bay Regional Parks, East Bay MUD, designated Open Space areas, Mt. Diablo State Park, etc. Check out the Alexander Lindsay Museum in Walnut Creek, where they do wildlife rehabilitation and they have animal exhibits that kids and adults will enjoy. John Muir's house is in Martinez, and Shadelands Ranch museum is in Walnut Creek.
Downtown Walnut Creek has dozens of restaurants of every description. There are a few familiar chain restaurants, some trendy upscale restaurants, some interesting ethnic places, and a concentration of Starbucks stores, a Peets, and a few smaller, non-chain coffee places. There are also bars and small clubs. Downtown Concord, around Todos Santos Plaza, has some good restaurants, too. Right on the plaza you can find the best Mexican food at Los Gallos, a good Thai place, and there are several more Thai restaurants within a few blocks. There is also a brewpub and a sushi place. On summer Thursday afternoons, there is a farmers' market and live music.