Not sure if this has been discussed before, but I couldn't find anything on it when I searched: Could Demonreach be built on the site of Yggdrasil? We know that there are roots there that go down lower than any plant puts down it's roots which seems like something that Yggdrasil could do. The leyline there has been referred to as the Well. Which brings to mind the Well of Mimir (which one of Yggdrasil's roots reaches into.) Odin taught Merlin. Merlin 'built' Demonreach. It just seems like a really good fit.