Final answer:
Yggdrasil's roots stretch to three significant realms in Norse mythology: Asgard, home of the gods; Jotunheim, land of giants; and Niflheim, a realm of darkness and cold.
Step-by-step explanation:
The mythical tree Yggdrasil from Norse mythology has its roots extending to three different realms. These three places include Asgard, the home of the gods; Jotunheim, the land of the giants; and Niflheim, a dark and cold realm. As Yggdrasil is a central element in Norse cosmology, it is believed that these roots support the structure of the universe, connecting the various worlds together and maintaining the balance.