The 20th annual Lollapalooza music festival held in Chicago ended day three with a downpour soaking attendees and a memorable performance by the Foo Fighters.

While weather held up for the first two days, the last day of the festival resembled a modern-day Woodstock, with Chicago's Grant Park turned into a massive mud slide as an estimated 90,000 concert goers were caked in filth from a heavy rainstorm.

Over 140 musical acts graced the 8 stages at the 20th anniversary of Lollapalooza, including Eminem, Coldplay, Muse, Cee Lo Green and Deadmau5, to name a few. Foo Fighters closed the show during a rainstorm playing tracks from their new album Wasting Light along with older hits.

Founded in 1991 by Perry Farrell, frontman of the alternative rock group Jane's Addiction, the sold-out Lollapalooza 2011 had a record number of attendees, estimated at 270,000. The event has since expanded to Chile and will launch its first show in Brazil next year, with more expansion in the future.