1 Draw a triangle

It will be the inner part of the Penrose Triangle.

2 Extend a line off of each corner.

3 Draw another line off each of thoose extensions, parralel to the nearest side, and that extends to the top of the corner.

4 Draw a short angle that lines up with the opposite side.

The size should be the same as in the previous steps.

5 Connect the lines, and ...
here it is !

So now let's play a little bit

For instance, we can reduce or enlarge the inner triangle ...

... or we can make it thinner or thicker

... or we can use a rectangular section, on one direction or another

... or we can even make an asymetric Penrose triangle