Mark your calendars shoppers, would-be retail employees and parents looking for a place where the kids can expend some energy. The largest shopping center now under construction in the Denver area will celebrate its grand opening Sept. 27. And its going to have an outdoor play area complete with a 30-foot-tall climbing structure to go along with its discount merchandise, developers say. The 330,000-square-foot Denver Premium Outlets broke ground at the northeast corner of Interstate 25 and East 136th Avenue in Thornton in October.