The realms of Norse mythology, connected by the World Tree Yggdrasil. They include Midgard (the human world), Asgard (home of the Aesir gods), Vanaheim (home of the Vanir gods), Jotunheim (realm of giants), Alfheim (realm of elves), Nidavellir (realm of dwarves), Helheim (realm of the dishonoured dead), Niflheim (world of ice), and Muspellheim (world of fire). Magnus Chase travels between these worlds in his adventures.