Urth is a fictional planet that serves as the setting for the science fiction series known as the Book of the New Sun by author Gene Wolfe. It is depicted as a far-future Earth, where the sun is dimming and civilization has regressed into a feudal society. The planet features a variety of landscapes, including deserts, forests, and cities, all influenced by the remnants of advanced technology. The inhabitants of Urth include various human cultures and other sentient beings, such as the Increate and the Cacogens. The narrative follows the journey of Severian, a young torturer, as he navigates the complexities of his world, exploring themes of memory, identity, and the nature of time.