Parmenides says that “nothing”, or the void, does not exist. That is, even if “what is” has limits, “what is” cannot move because that would require that it moves into the void. The void, being nothing, cannot be moved into.
Democritus was the first we know to record atomism in more detail. He believed everything is composed of an infinite number of these “somethings.” They are in constant motion and have an infinite possibility of shapes and such. “What is not” is simply whatever is not an atom. “What is” is simply whatever is an atom. Therefore, the void is a space into which “what is” can move into. Parmenides would have disliked this, of course.
Either way, it wouldn’t look like anything.