Buildings and constructions that cannot be made in real life.
These drawings make connections which aren't actually possible in real life.
Endless staircases where you can keep going up, down or all sides forever.
Geometric planes or surfaces with errors which aren't possible in reality.
You can draw these shapes, but they can't actually exist. Typical for these illusions is that you can't color them without coloring the background.
These drawings start out with one subject, and fluently become something completely different. Yet you can't really tell where the transition happens.
A nice art form with great illusons from another reality.