How to build an impossible triangle out of wood. This video shows the basic shape. Instructions are below.
This is made using three pieces of square cut wood. 20mm by 20mm. Two pieces are 70mm long and the other is 90mm long. Cut one end of the 90mm piece so that it lines up with the other sides of the triangle when viewed from the correct angle.
The pieces are joined together at 90 degree angles. Painting the sides using three slightly different shades can enhance the illusion.