A remarkable chemist and popularizer of science, Ilya Leenson was the author not only of many books, but also of unique problems, most of which he came up with for the Moscow Intellectual Marathon and Summer Linguistic Schools. Now they are combined into one collection, and the reader has the opportunity to get acquainted with these witty and non-standard problems from a variety of fields of knowledge - from astronomy to chemistry, from Russian poetry to Scandinavian mythology, from cryptography to numismatics. Sometimes resourcefulness and common sense are enough to solve them, but often erudition or short mathematical calculations are required. The answers, in fact, are fascinating popular science notes that refute the stereotype about the strict division of sciences into humanities and natural sciences. The book will be of interest to schoolchildren and anyone who wants to test their intellect and broaden their horizons.