"The Horror-Horn" is a short story by E.F.Benson.
Summary
THe story focused on a man, who vacations in the swiss Alps, around the Ungehoerhorn Mountains. He is met by a friend who relates a tale of his meeting with a local barbaric tribe of semi-human things, primitive and ape-like in all but its human features.
Days later, the man wanders in the forest and meets an old hag of these people. He manages to escape it, but he is horrified beyond his wits.