Walter Reed Medical Center in Washington, D.C., was the flagship medical center for the U.S. Army and served more than 150,000 active and retired military personnel until its recent closure. The Walter Reed Community Center (pictured) employs an extensive green roof of lightweight plants. Col. Charles Callahan, commander of DeWitt Army Community Hospital and Health Care Network, says that research has shown "that in the presence of scenes of nature, you actually require less pain medication after surgery.”