4. Minnesota Twins, Target Field. Now under construction, this Minneapolis landmark is scheduled to open in 2010. Like the Nationals, the Twins are committed to achieving a LEED rating, and coughing up $2.5 million extra to do so. Green features include such basics as low-VOC carpets and paints, and the club is using local building materials. But more important may be the site itself: Unlike, say, the Mets stadium stuck out in Flushing, Target Field sits right downtown. Reinventing a plot in the city’s warehouse district, the Twins are creating an attraction that will be walkable, bikeable, trainable, and busable for thousands of local fans.