The Cult
No one ever built Fenrir an altar. The wolf is the one great power of the North with no cult at all: no sanctuary, no votive deposit, no runestone invokes him, and Snorri gives the reason inside the myth itself — the Æsir would not stain their holy places with the wolf's blood, so they bound him instead of killing him. His only 'temple' is the binding: the isle of Lyngvi, the slab Gjǫll, the boulder Þviti. The nearest thing to worship the tradition records is the fear that attends his name and the idiom born of it — to break loose from Lœðingr, to dash out of Drómi — which Snorri says passed into the language itself. Viking-Age Christians read him on their crosses at Gosforth and Kirk Andreas as prophecy, not prayer. A few modern Heathen groups reverse the judgment and honor him, but the mainstream of the revival keeps him as the bound doom, not an object of cult. The evidence is thin because the tradition wanted it thin: Fenrir's role in northern religion was to be the thing religion held at bay.