The Klein Bottle is a mathematical joke, a surface with only one side. Just as it's about to enclose a space like a regular bottle, it curves back with a twist so the inner face merges with the outer, and suddenly inside and outside become one, like the sides of a Möbius strip.
This neat trick of geometry can't quite exist in three dimensions, since the surface has to cross through itself, but at least we can make models to see how it works. This one is 3D printed in stainless steel with some bronze for color. It's durable, washable, and ergonomic, sized to fit the hand sweetly.
The perfect finishing touch for any math fan's kitchen, and you don't have to study geometry to enjoy it.
Yes, it really opens bottles!
Klein Bottle Opener, bronze finish 3" tall - $72
Pewter finish - $72
Perhaps of historical interest, the first version of this page. I might have opened a bottle too many before I wrote it.