Throughout the Eastbay, you won't find a more instantly recognizable location from such incredible distances as Mount Diablo. While the shoulders of this giant mountain are broad and sloping, don't be fooled, the plethora of hiking trails can be quite difficult and steep in some places. Mount Diablo can best be accessed by getting off of HWY 680 at either the Los Cerros or Diablo Road exits and weaving through Danville's eastern side, meandering through snake-like turns in an incredibly picturesque countryside until you reach the 3-way stop near Athenian School. From here, head north and simply follow the zig zag 2-lane mountain hike up to the summit- but watch out for the constant, ever-streaming cyclists who daily make this mad journey up-hill(or whiz down it at ultra-high speeds after reaching the summit).
Located just 5 minutes past the Park Ranger's entrance, you'll come across the first of 2 campgrounds - Live Oak - which is positioned within walking distance from one of the funnest areas of Mount Diablo: Rock City. Here the kids (OK, the adults too!), can scale and crawl around all sorts of amazing jutting rock formations. Once atop, you'll command sweeping views, in any direction, of the entire Eastbay. The campground itself is somewhat basic and is not that much of a draw, other than being a really convenient respite from the tons of trails and activities that abound on this mountain. There's a community amphitheater, which leads me to believe that perhaps the Park Rangers lead educational seminars, but none have ever been offered while we've been there.
The best bit about Mount Diablo is that for a 20-25 minute drive up to the campground, you really do feel like you are getting away from it all, and the upside is, well, you're on a mountain, so you've got incredibly great views all the way around- you simply need to do a little bit of homework in terms of which trails to target. Scattered throughout Mount Diablo are really great(especially now during C19) isolated picnic areas and benches to avoid any crowds (which you'll definitely come across either at Rock City or up at the Summit). I highly recommending ascending to the Summit for a 360 degree view of the Eastbay, where on a clear day, you can catch a glimpse of the Sierra Nevada mountain range, San Pablo Bay as well as even certain peaks at Yosemite.
And while we all love hot dogs and cooked beans, followed by S'mores, the great thing about this campground is it's proximity to civilization. If you get tired (or run out) of campground fare, check out the few restaurants in nearby Blackhawk (turn left after Athenian School) or a myriad of options in Danville (turn right and head back to and past HWY 680), of which I highly recommend Locanda Ravello for old school Italian (ask for Antonio!), Luna Loca for the best Mexican around (for those that appreciate real heat, try anything 'pica'), farm-to-table Harvest or the outdoor patio with live music at Bridges.