THE CLOSEST YOU’LL GET TO A 4D OBJECT IN OUR UNIVERSE A Klein Bottle is a 4-dimensional shape that has neither an inside nor outside. Like a Möbius strip, if you trace a path along its surface, you will travel on both sides of the surface before returning to the starting point. In the mathematical field of topology, it is a 3D immersion of a closed, one-sided, non-orientable, boundary-free manifold. A true Klein Bottle does not intersect itself, so it can only fully exist in 4 dimensions. But in the same way a 2D shadow is cast by a 3D object, this can be considered the 3D “shadow” of a 4D Klein Bottle—the closest we can get in our universe. A perfect gift for a math or science enthusiast.