I saw some very wide and long but shallow Sterilite containers with
smooth and shiny clear sides at the local megastore recently.

My cats have no problem jumping into (and out of) them, no matter how
high they are. The first time, I used a block of something so that
they could step up. With my current rescue, I didn't bother and she
jumps into it just fine (even though she has sometimes jumped up onto
the side first).

It beats a covered litter box. Besides not needing cleaning (for some
pleasantly strange reason), they're huge, too, giving the cat lots
more room. When exiting, the impact of hitting the Astroturf probably
removes more litter from their paws, too.

It's weird that stuff just doesn't stick to the sides of them, at
least not for long. They look shiny smooth after about a year. I
doubt that the Arm & Hammer Essentials Natural cat litter helps keep
them clean, but who knows. I think it's the type of plastic.