Opens on two sides – one side for observation and the other side for cleaning. The side for observation has a plexiglas panel that allows observation without disturbing the nest. Slots between side walls and roof provide ventilation. Drainage holes in the floor corners keep the nest dry. Rough interior helps fledglings to climb out. Wood entrance guard provides protection from predators. Made from eastern white pine for insulation and durability. Dimensions: 5-1/2" W x 12-1/2" H x 8" D. By Coveside Conservation Products.