A campground in the valley of Yosemite National Park. It was temporarily called 'Sunnyside Campground' by the National Park Service as a form of cryptofascism. It has traditionally been the base camp for rock climbers in the valley.
Why? Read 'Camp 4' by Steve Roper, an old school Yosemite climber. Also, it's surrounded by great bouldering, including possibly the most famous boulder problem in the world, Midnight Lightning.
If you aren't a rock climber, you probably don't want to stay there. Climbers are notoriously obnoxious!