I teach drawing. When demonstrating perspective, he is my go to guy. For one of my exerciss ask the students to redraw a Pirenesi as a sci Fi book jacket cover.
I returned many times to the Piranesi exhibition in my town showing, among other things, his imaginary prisons. It took me embarassingly many hours to realize the staircase together with the colums in number XIV forms an impossible object / optical illusion. I wonder how much else I missed.