I have a 4-5 month old kitten that loved sleeping in the litter box. The first time I saw him in there, I had to quickly step out of the room so he wouldn't see me laughing at him! I think he finally caught on that the LB isn't so great...now he sleeps in potted plants.

No surprise that he was found in the great outdoors as a hungry little stray..... If your cat has never been an outside cat, it could be that he/she just find the litter nice & comfy. It's probably like when you're lying on the beach and you get the sand *just right* under your body. ahhh...