The Shinjuku Sumitomo Building was built in 1974 in Tokyo’s Nishi Shinjuku district. The site’s expansive “Sankaku Hiroba” (triangular plaza) atrium roof, along with associated renovations, offers a sustainable model for addressing an emerging problem for Japan’s cities: how to carry out renovation projects on large-scale buildings using good maintenance practices. The project also represents a greater societal effort to enliven the urban business district and enhance its value as an accessible gathering place.