Watch yourself visibly grow and shrink or make a friend look tiny alongside you.
The Ames Room is a deformed room that creates an astonishing illusion. When you look inside, although the room is heavily distorted it appears completely normal with parallel walls and horizontal floor and ceiling.
This is because the brain has been conditioned to assume that walls of rooms are parallel. The assumption is so strong it completely overrides the fact that people are changing size, even though in the real world this obviously doesn’t happen. Here your brain is willing to accept it as the assumption of parallel walls is much stronger!