Beginning of the cube inversion.
(J.P. Petit & C. Tardy)
This is the polyhedral version of Morin's initial "practical joke" inversion model, whose central structure is a two-sheeted covering of Boy's surface. For now (April 2000), I've only found this, but Christophe Tardy quickly transformed my cardboard model into a new entry in the menagerie of virtual reality.
To be continued...