Belluna Dome is a baseball stadium located in Tokorozawa, Saitama, Japan. It is home to the Saitama Seibu Lions, a professional baseball team.
The stadium has a roof over the field and the stands, like other indoor ballparks. However, it lacks a wall behind the stands so that natural air comes into the field. This makes it possible for home runs to leave the stadium, something not possible in typical domed stadiums. From Wikipedia
