Hold your mouse over the picture to rotate the triangle and solve the mystery of the Penrose triangle or Penrose tribar. The Mathematica Code: (see also the Mathematica project *)
b=N[20/7];d=22.4;f=18.666;h=20;
P1=Cuboid[{{0,0,0},{h+b,-b,b}}];
P2=Cuboid[{{0,0,0},{b,-h,b}}];
P3=Cuboid[{{0,-h,0},{b,b-h,f}}];
P4=Polygon[{{b,b-h,f},{b,-h,d},{0,-h,d},{0,b-h,f},{b,b-h,f}}];
P5=Polygon[{{b,-h,f},{b,-h,d},{0,-h,d},{0,-h,f},{b,-h,f}}];
P6=Polygon[{{0,b-h,f},{0,-h,f},{0,-h,d},{0,b-h,f}}];
P7=Polygon[{{b,b-h,f},{b,-h,f},{b,-h,d},{b,b-h,f}}];
S=Show[Graphics3D[{P1,P2,P3,P4,P5,P6,P7}]]
The object on Shapeways for printout.

A page from the book "A topological picture book" by George Francis.