This is a free 24-hour music festival in Shanghai's nearest watertown, Zhujiajiao, featuring a bunch of Shanghai-based DJs and a couple of bands. The organisers expect about 300 people to come down. Music starts Saturday at 4pm and doesn't stop for 24-hours. There are places to camp, plus BBQ pits, games for kids and some other nearby activities. Full details about how to get there and who's playing is at the end of this link.