In high school we regularly threw 100+ person parties under bridges and along the river, in random lots, wherever we could, really. However, it required a lot of coordination and trust between a lot of people to avoid surprise police encounters, and the local police personally had me and some of my associates on their shitlist which further complicated things. It was an environment I thrived in, but I wouldn't want my child to have to encounter the same level of risk and paranoia just to hang out with their friends.