Floating Cube

To see depth, the brain measures perspective from front to back, like lines receding into the horizon. Most of the time it’s right. But not in the case of this illusion. You might need to watch it twice. If you want to learn more about optical illusions, you should check Sophia Williams’ book, 3d Drawing and Optical Illusions: How to Draw Optical Illusions and 3d Art Step by Step Guide for Kids, Teens, and Students.