The World Within is the third scenario in The World Tree, the fifth part of Heroes Chronicles. On their way to find the World Tree, Tarnum and the barbarian tribe come across a large cavern with trees, grass, and flowers, despite the fact that they are deep underground and there's no sunlight or rain here. Even the shaman Addar has never heard about anything like this, but he guesses that it's due to the influence of the World Tree.