An extension for set number twenty (20A) includes 300 stone blocks in the three standard colors; brick red, natural sand, and slate blue. The Designs for Architectural Models booklet includes eight building plans for large and complex buildings including a Gothic cathedral and a castle and bridge. Packaged in the traditional wooden box for storage with a packing diagram and construction templates. This expansion allows you to build the largest and most complex models. This set plus the combination for set #20 becomes the equivalent of set #22 and allows you to build all of set #22 models.