The popular book "Kalejdoskop matematyczny" by the famous Polish mathematician G. Steinhaus is devoted to "entertaining" questions of mathematics. Usually in entertaining books on mathematics there is a lot of extraneous material, humorous stories, etc., which have nothing to do with mathematics. In the same book, the author with great taste selected only mathematical material and presented it to the reader in a form that develops his curiosity and inquisitiveness. He identified from a large number of mathematical ideas and concepts those that are most easily amenable to a convex, visual image that requires only minimal verbal explanations.