Parallel-universe box

Description
The Parallel Universe Box is a box that was accidentally created by Professor Farnsworth. At first it was going to be thrown into the sun and no-one was allowed to look in it but it was later discovered to have a whole parallel universe inside. Professor Farnsworth in the parallel universe also created a blue box containing our universe. Afterwards more boxes were created containing other parallel universes. The two main boxes were switched so they contained their own universe.

Appearances
"The Farnsworth Parabox" (4ACV)