6. Alpine Valley Music Theatre, East Troy, Wisconsin
Jam bands have flocked to this sprawling outdoor space, just outside Milwaukee, ever since the Grateful Dead started playing here in the Eighties. (Deadheads loved Alpine Valley, in part due to the site's generous camping arrangements.) And not just jam bands in the strict sense of the words: In 2011, this is where Pearl Jam chose to celebrate their 20th anniversary with a two-day blow-out. Andy Cirzan, vice president of concerts for Chicago's Jam Productions, still has fond memories of a Rage Against the Machine show that "turned 35,000 fans into a surging, amoeba-like entity that moved and grooved in flowing waves like nothing I had ever seen before."
Fun Fact: Alpine Valley had to make serious structural repairs after the summer of 1989, when the grounds turned into what one local critic called "a muck-filled slip 'n' slide" that actually trapped fans overnight in their cars.