It looks like a hollowed-out baked potato, but it's actually a German cat cave. Meet the katzenhohle. They are hand-made, according to ModernCat, and can be purchased at Germany's equivalent of Etsy, the crafting site DaWanda. I'm guessing that the cats rather enjoy these katzenhohle.
They are remarkable in many ways, not the least of which is that the cat sleeps inside a contraption that looks a whole lot like something the cat threw up.