Prepare to waste at least 3 mins trying to figure this thing out. It is called the “Klein Bottle” and has no inside nor outside surface, what is more you can actually fill these with fluid. Here’s how

Klein bottle If you want to give a mathematician something to try to wrap their head around, a Klein bottle is a good place to start. A real Klein bottle is an object with no inside and no outside.

A Klein bottle is a surface which has no edges, no “inside” or “outside” and cannot properly be constructed in three dimensional space. This bottle, from a series made by Alan Bennett, was constructed as accurately as possible.

This is one of a series of glass Klein bottles made by Alan Bennett in Bedford, United Kingdom for the Science Museum, London. It consists of three Klein bottles, one inside another.

World's Smallest Klein Bottle by kivaford on Etsy

There's no better knick-knack for your burgeoning collection of tiny objects than the world's smallest Klein bottle. This self contained bottle is.

The Klein Bottle, first conceived of in 1882 by German mathematician Felix Klein.

The Klein Bottle, first conceived of in 1882 by German mathematician Felix Klein.

Klein bottle: "In mathematics, the Klein bottle is a non-orientable surface, informally, a surface (a two-dimensional manifold) in which notions of left and right cannot be consistently defined." // Seen in: wormholes (hopefully)!

The Klein bottle, a "non-orientable" object, much like a Mobius strip, at least to the extent than I understand it.

genuine glass Klein Bottles. These are the finest closed, non-orientable, boundary-free manifolds sold anywhere in our three spatial dimensions.    These elegant bottles make splendid gifts, outstanding classroom displays, and inferior mouse-traps. With its circle of singularities, an Acme Klein Bottle can be said to exist inside of itself -- especially handy during time-reversals.

Acme Klein Bottles - amazing one-sided bottles and other mathematically interesting products

Klein Bottle House on the Mornington Peninsula in Australia, designed by architects McBride Charles Ryan.

Klein Bottle house / McBride Charles Ryan

Cliff Stoll behind the meter tall Klein Bottle

Acme Klein Bottle makes and sells glass Klein Bottles.