The Walk on the Hill & Green Expo takes place Sunday, April 30, from 2-5 p.m, Windover Heights Historic District at Windover Avenue & Orchard Street. Part of the Walk on the Hill event, sponsored by residents of the Windover Heights Historic District and Historic Vienna, Inc., Green Expo will feature alternative fuel vehicles, James Madison High School environmental programs, home energy audit demonstration, e-recycler and composting companies and Town of Vienna greenhouse propagation discussion.