This year marks the 20th anniversary of Lollapalooza, the celebrated festival that has come a long way in the past two decades. It's evolved from an alternative music tour to a cross-genre mainstay in the summer festival circuit, where concertgoers happily brave the 100-plus-degree heat index with a gourmet hot dog in one hand and a pint of locally brewed beer in the other. A lot has happened during the history of this iconic event, so as its birthday approaches, we take a look back at Lollapalooza's most memorable moments.