An Ames Room uses forced perspective to make people appear like giants or dwarves depending on where they stand.

The Ames Room was invented by American ophthalmologist Adelbert Ames Jr. in 1946, based on concepts first described by Hermann von Helmholtz in the late 19th century. The room is constructed so that from the front it appears to be an ordinary cubic shape with parallel walls and a level floor. In reality, the room is a trapezoid where one corner is much farther away from the observer than the other. The floor and ceiling are built at precise inclines to maintain the optical illusion of a standard rectangular room. When an observer looks through a specific monocular peephole, the brain applies 'size constancy,' a psychological phenomenon where we perceive objects as having a fixed size regardless of their distance. Because the brain is convinced the two people are at the same distance from the eye, it interprets the difference in the image size on the retina as a difference in physical height. This effect is so powerful that it overrides our logical knowledge that people do not suddenly grow or shrink. Research at institutions like the University of Exeter has shown that the illusion persists even when observers are aware of the room's true shape. Beyond psychology labs, this technique was famously utilized by cinematographer Andrew Lesnie in Peter Jackson’s 'The Lord of the Rings' trilogy. By using 'forced perspective' sets, the production avoided expensive digital effects to make actors like Elijah Wood appear significantly shorter than Ian McKellen.