Sketching this one on paper was not very hard, but when drawing it on the computer it got a bit complicated. In this design all of the sides depend on what they are connected to, so basically if you increase the width, height or length of any part of this figure, you have to redraw the entire thing.
Update: This figure has been updated, so it no longer completely matches the one Loniek painted on his walls. The lines are still the same though.
This already impossible tribar interconnects at the center to make up three impossible rectangles.