The Klein Bottle claims to be "the closest you'll get to a 4D object in our universe," and while I don't really understand what that means, I'll make a note to ask the Bing AI Chatbot about it later. What interests me more, though, is that the Klein Bottle also says it doesn't have an inside or an outside, which I do understand, but can't really comprehend. I'm only looking at a photo of it, but, like, I can see an outer surface. And since the bottle is made of transparent glass, I can also see an inner surface and empty chamber.
But the Klein Bottle explains this away, noting that, "In the mathematical field of topology, it is a 3D immersion of a closed, one-sided, non-orientable, boundary-free manifold." So here we are. Back to things I don't understand again.
One thing that makes perfect sense, and that also makes me feel much better, is that the Klein Bottle is marketed as the perfect gift for a math or science enthusiast. And I am most definitely neither of those. So ye dudes and ladies who are, and who get 4D theory, and who also get that this here 4.3" piece of hand-blown glass is really just a 3D "shadow" of a 4D object, go on then. Get yourselves a Klein Bottle, and bask in your proximity to the 4th dimension.