The theory of relativity and the Pythagorean theorem
by L. B. Okun
[Physics Uspekhi 51, 622 (2008)]
Although written at an "introductory" level, this is
(like many of Okun's popular-science
articles) really very sophisticated
and worth the attention of people who
may think they already know the material.
Special relativity
by Andrey Grozin
[2011/08] In Russian, and aimed at "school children", who perhaps
have a somewhat stronger background in Russia than in the US.