In this month’s issue of the American Mathematical Monthly, there is a review of a series of animated videos about geometry, called Dimensions. The aim of the videos is to introduce the geometry of 4-dimensional space, and in particular the 3-sphere which we can view as living in 4-dimensional space. I haven’t finished watching the entire series, but what I’ve seen so far is pretty impressive. The entire series runs about two hours. It is freely available on youtube — see below for the first installment.