At the original Shady West in Wallingford, I built an elaborate slanted walkway to allow our cats to come up along the side of the house and in through a cat door installed in my office window. The unsightly contraption had to be hastily dismantled when we were selling the house.
Now I discover there's an international website (blog) devoted to photos of elaborate stairways and other structures providing indoor/outdoor cats with access to homes.
Not all cats need ladders. This one climbs stucco!