This is a rather interesting angle (pun intended) on Special Relativity written by L.B. Okun.
Abstract: It is shown that the most important effects of special and general theory of relativity can be understood in a simple and straightforward way. The system of units in which the speed of light $c$ is the unit of velocity allows to cast all formulas in a very simple form.The Pythagorean theorem graphically relates energy, momentum and mass. The paper is addressed to those who teach and popularize the theory of relativity.
It is a continuation of his earlier article.
Some parts of it are rather confusing, at least to me, since he did not write very much in most of the smaller sections of the article. There were times that I wished he would elaborate a little bit on what he's saying, especially if he's intending this article to be read by people teaching relativity.
Read it and tell me what you think. If nothing else, one gets a rather brief and useful history behind the development of SR.