What you describe sounds similar like the Underworld of Homer. The Greek king Odysseus sails far to the west and finds the edge of the lands of the dead. There he performs a blood sacrifice to call the souls of heroes to him and give them back their power of speech so he can confer with the seer Tiresias.

If none have returned from Aman, is it just taken on faith that the fëar of the fallen have been called there?