The Mother Tree, The Divine Tree, Tree of Life, The World Tree... It has many names. This is the Ash Tree named Yggdrasil and it is the massive structure that holds the multiverse together. Yggdrasil actually lives in the Astral Plane, but is so massive, that her branches and roots penetrate into a majority of the other planes. The Mother Tree of Galifar is just a single branch of the cosmically sized ash tree as the other parts of the tree spread to other planes of existence. Spiraling along the branches main trunk, planks and sets of steps were carved or mounted onto the tree by many generations of druid that worship the tree to assist them in climbing to the upper canopy which is about 1 mile high and 3 miles across.
Yggdrasil is a silver-barked ash tree. Its leaves are blue-black and oval shaped and its rough bark resembled flaking gray clay. It is made of a type of divine wood that was immune to fire, although fallen branches and leaves could be safely used for cooking fires. Spiraling along the main trunk, planks and sets of steps were carved or mounted onto the tree by many generations of druid that worship the tree to assist them in climbing to the . The druids say that the tree was once surrounded by sky in all directions before the planes developed. It is said to have produced fruits which the druids clam became all manner of life in the cosmos.
The entire tree is 23 miles tall, with a 15‑mile-wide canopy. Its trunk is 4,000 feet in diameter at the bottom, but tapered down to a diameter of 1,200 feet at the point where it started to branch. All branches of the tree resembled enormous trees themselves, extending form a half a mile to up to 10 miles high, depending on which plane you're in. Many, but not all of them ended in two-way portals, or the color pools, a term coined by denizens of the Astral Plane. Since there are many dead ends along the tree's branches, traveling without a guide or directions often results in long detours or worse.
Because a vast majority of Yggdrasil actually exists in the Astral Plane, if traveling from Color Pool to Color Pool, one would pass through the Astral Plane to reach the next Color Pool. Climbing the tree through the Astral Plane is difficult, but it was possible to get better footing by wearing spiked boots. The trip was made more perilous by the fact that gravity was not constant along the tree. The Astral Plane does not have gravity, but Yggdrsil is so massive, she has her own gravity. Throughout most of the trajectory, it points towards the center of the tree's trunk, but it slowly changes to match its destination plane as one approaches a portal. It was usually possible to predict when gravity would change by observing the direction of the moss growth along the trunk.
Once on Yggdrasil, it was said that a trip from the highest branch in Elyseum all the way down to the lowest root in Hades took at least 100 days, but there was no record of any mortal ever successfully completing the journey. On the other hand, trips between nearby Planes, such as Asgard to Limbo rarely took longer than a week. In both cases, those trips were not without risks, either from the tree's inhabitants, from the risk of falling into the Astral Plane as a result of losing contact with the tree's branches, or from simply walking into the wrong destination by mistake.