Giant spiders and tiny people, bloody battles of ants, desperate battles of microbes, travel inside the human body and unimaginable universes contained in atoms - penetration into the microworld has long been the cherished dream of science fiction writers. The book of the classic American literature M. Twain “Three thousand years among microbes" continues in the "Polaris" series the publication of forgotten and rare works, united by the common theme of "adventures in the microworld." The book includes the fantastic story “Three Thousand Years Among Microbes” and fragments of the unfinished novel “The Great Darkness.”