Offshore Rooftop 1000 E Grand Ave, Chicago, IL 60611, USA Celebrate Halloween at Offshore Rooftop with live DJs and sweeping Lake Michigan views. Costumes encouraged. Halloween at Offshore Rooftop Celebrate Halloween at Chicago's largest rooftop with a night of music, costumes, and unforgettable skyline views. Join us Saturday, October 31, for an elevated Halloween party featuring live DJs, high-energy dance music, curated cocktails, and one of the city's best crowds. Overlooking Lake Michigan and the Chicago skyline, Offshore Rooftop transforms into the ultimate Halloween party.