Instead of buying a ready-made tunnel for your model railroad, consider making your own customized tunnel. To make a tunnel all you need to do is to bend chicken wire into the shape of a tunnel and wrap it all over with plastic sheet. Now, cut newspapers into 1 inch wide strips and dip it in colored plaster slurry. Cover the chicken wire frame completely with the help of this soaked plaster paper strips and with the help of a modeling plaster mold the shape of a mountain over this plaster. Once you have allowed this to dry completely, paint the mountain according to your railroad theme and add surrounding accessories like rocks, dirt, grass, stones etc.