architecture construction fire exit flight of winding stairs grate grated helical metal security shape shapes spiral stair staircase wentletrap asphalt barrel build building bulldozer caterpillar dig digger excavator lay machines not ready road roller steam track work bolt concrete construction-work cylindrical delayed foundation neglect neglected rust secure set stability stable strong thread turns twist brick bricks brickwall brickwalls brickwork brickworks cracked house mortar old stone stones sundbricks texture tile wall half-timbering timber wood