The sphericon is a solid that has a continuous developable surface with two congruent semi circular edges, and four vertices that define a square. It is a member of a special family of rollers that, while being rolled on a flat surface, bring all the points of their surface to contact with the surface they are rolling on. (Wikipedia)
I designed this after looking at a youtube video....
There have to be 2 prints of this object and they have to be glued together 90° turned.
I did print it and glued it.