Roots

The Roots are the starting point of all climber's adventures. They tether the World Tree Yggdrasil to the terrestrial world and provide the outside world necessities such as water, air and vegetation.

About
There are 4 major roots that span across the outside world that correspond to the direction of: North, East, South and West; therefore there are 4 different entrances to the World Tree. Other than the 4 major roots there are other roots that kingdoms, towns and villages are built around as they provide excellent and refined resources for the outside people.

As the roots are not impenetrable like the bark of the World Tree, civilisation has used the materials of the roots to invent all kinds of useful things.