Umbra : The Velvet Shadow — Daniel Greenberg

Werewolves still live between the two worlds. They have one foot in each, yet their home is neither. Great adventures await in the Umbra - but so does death; the Wyrm has infiltrated the Shadow. The Apocalypse is coming, even in the spirit world. Umbra: The Velvet Shadow is a Werewolf sourcebook detailing the places, spirits and cosmology of the Garou spirit world.