Lastly, I found the impossible cube also quite compelling. It is a derivative of the Necker Cube, however this illusion is more obviously meant to be viewed as a 3d object. Additionally, it is also interesting to me for its resemblance to a tessaract, an object associated with the 4th dimension theorized of by mathematicians and philosophers for quite some time. The tessaract is the 4th dimensional analogue to the 3 dimensional cube.