A friend who was renting my loft had a cat who didn't get along with mine (and they were also indoor) so I built this cat ladder. There's a sheet of plexiglass on the front and carpet is on the treads. A ramp at the top that's perpendicular to the other ones led to a cat door on the second floor and there's another at the bottom. I set up a camera to capture this video of it in action. Enjoy!