A few months ago, my wife and I adopted three adorable rambunctious kittens. Before S.A.N.T.O.S. Six Toes, Herbie the Love Bug, and Trey, were old enough to explore the outdoors, we decided to extend our eight-year-old standard-sized catio. We added a bridge and a large 3-level triangle-shaped enclosure above our backyard kitchen sliding glass window.
More info here: https://www.customcatios.com/catio-guy-personal-catio/