A mathematician named Klein
Thought the möbius strip was divine.
He said, "If you glue
The edges of two
You get a weird bottle like mine."

You can get 3D approximations of a Klein bottle (with a hole) from http://www.kleinbottle.com/; you can also see how to knit them, without a hole (from a certain point of view) at http://web.meson.org/topology/.