First Appearance: Shadow Raiders
Description: Wyrmhole Generator/Nexus
Summary: Norse mythology references Yggdrasil as the Tree of Life, a Mighty Ash growing in the heart of Asgard, with its roots reaching into other realms and its branches supporting many of the nine realms.
In 2016, an ancient doorway was unearthed in Greenland, sealing a Wyrmhole that led to the alternate reality of Asgard. This portal was the none other than the true Yggdrasil.
Carved from an obsidian plain, Yggdrasil is a series of canyons, cut in the shape of a tree, fed by the river Hvergelmir. The "tree" itself is a massive Wyrmhole nexus, with each of its eight paths leading to different planes of reality, including Earth, or Midgard, as the inhabitants of Asgard call it.
Presumably created by the Fallen Angel Aurg-el, Yggdrasil connected the world of Asgard to other alternate Earths, awaiting the day that Aurg-el's horde of Fell warriors could unleash the apocalypse across all of reality.
Following the Battle of Asgard, the gates to Earth were secured by US Armed forces and a team of thaumatologists continues to examine Yggdrasil--although opening any of the other sealed passages is strictly prohibited.
Author's Notes: Shadow Raiders has been in the works for two years now--fleshed out from notes I started back in 2014. The concept for a spinoff line of books from Stone Soldiers, taking the battle to the monsters where they live, has evolved over that time, but the core principle of Yggdrasil as a portal between worlds has remained.
As a plot device, Yggdrasil is invaluable--a magic gateway, much like the wardrobe in Narnia, allowing exploration of other realms. Unfortunately, seeing as how Midgard and Asgard have no been established, there are only seven other worlds I can explore in the series--assuming it does well enough to go that far. Only time will tell...