Our house has a utility room in the middle of the basement. This is nice for keeping the various pumps and heaters seperate from the living space, but unfortunate in that it cuts the basement roughly in half. We "fixed" this problem by cutting some holes in the walls. The tunnel is roughly defined by the 2x4 frames that we put up, with a plywood "roof" tall enough for an adult to sit, or a child to stand. Teddy sees nothing remarkable about this.