IBIYAYA Backpack. $100.00 Cash only. (New is $164.00) Can handle 2 cats, one extra large cat, or one small dog. Can open into one large compartment or separate into 2 compartments. I used with one cat in the top compartment and my own things in the bottom compartment. Comfortable straps. Top and front windows can open completely or can be closed with strong see-through mesh. Top also has a solid flap that can be closed. Several pockets.
Google "Ibiyaya two tiered pet backpack" for more detailed information and photos.