The remarkable chemist and popularizer of science Ilya Leenson was the author of not only many books, but also unique problems, most of which he invented 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 various 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 erudition or short mathematical calculations are often required. The answers, in fact, are fascinating popular science notes that refute the stereotype of a strict division of sciences into the humanities and the natural. The book will be interesting for both schoolchildren and anyone who wants to test their intellect and broaden their horizons.