The free event will begin at noon. The first 365 attendees dressed as the green-faced Elphaba, the not-so-wicked Witch of the West, will receive a pair of tickets to a future performance of the Stephen Schwartz-Winnie Holzman musical. Dee Roscioli, who currently heads the Chicago company as Elphaba, will lead the crowd in a group sing-a-long of the Act One finale, "Defying Gravity."

Water Tower Park is located at the corner of Michigan and Pearson.

The open-ended Chicago production of Wicked began performances at the Ford Center for the Performing Arts' Oriental Theatre June 24, 2005, and officially opened July 13. The original Chicago company included Ana Gasteyer and Kate Reinders as, respectively, the gravity-defying and "Popular" witches.

Based on Gregory Maguire's novel, which turned every Oz myth inside out, Wicked — with a score by Stephen Schwartz and a book by Winnie Holzman — explores the early life of the witches of Oz: Glinda and Elphaba. The two main characters meet at Shiz, a school where both hope to take up sorcery. Glinda is madly popular and Elphaba is, well, green. By a misunderstanding, they wind up roommates and, after an initial period of mutual loathing, begin to learn something about each other. Their life paths continue to intersect through a shared love, entry into the Emerald City and interaction with the Wizard himself. Eventually, their choices and convictions take them on widely different paths.

Chicago's Ford Center for the Performing Arts/Oriental Theatre is located at 24 West Randolph Street. Tickets for Wicked are available at all Broadway in Chicago box offices (22 W. Monroe Street, 24 W. Randolph Street and 151 West Randolph Street) or by calling (312) 902-1400. For more information visit www.wickedthemusical.com/chicago.