Nationals Park, the home of Major League Baseball's Washington Nationals, became the country's first LEED-certified major professional sports arena when it opened in March 2008. With high-efficiency field lighting that saves 21 percent on energy costs, water-saving plumbing that cuts water consumption 30 percent, and construction materials made of at least 10 percent recycled content, this ballpark is a green grand slam. Plus, it's easily accessible by D.C.'s Metro rail and bus transit services.