 It was held on October 20 and October 21, 2006, with an optional trip to Adler Planetarium's TimeSpace show for attendees on October 22.Due to that year's Chicago Marathon, attendees unable to stay downtown were provided free passes to the Chicago 'L' railway system for the weekend (an arrangement referred to as "Plan 'L'").The second C4 conference was held at the Chicago City Centre Hotel on August 10–August 12, 2007.