The mythical tree that connects the heavens, earth, and underworld is known as Yggdrasil in Norse mythology. This immense, sacred ash tree serves as the axis mundi, linking the nine realms of existence. It symbolizes the interconnectedness of all life and plays a central role in maintaining cosmic order. Yggdrasil is home to various creatures and beings, highlighting its significance as a vital source of life and a representation of the cyclical nature of existence.