In Celtic mythology, the sacred tree believed to connect the realms of the living and the dead is known as the Yggdrasil or Tree of Life. This mythical tree serves as a vital link in the cosmos, with branches that reach to the heavens and roots that extend into the underworld. It represents the interconnectedness of all life and the balance between realms. The Yggdrasil embodies themes of growth, wisdom, and continuity, serving as a reminder of the cyclical nature of existence in Celtic belief systems.