In Überwald, this is the river that runs through the region of Klotz. Not the River Um or the River Eh, you understand, but the River Ah. Shortly after a vampire corrected this small but important point for Nanny Ogg, he was rewarded with an orally administered lemon. However, according to Mightily Oats' seminary lecture notes about vampire-slaying, Deacon Thrope insisted that the correct way to despatch a vampire in the Ah Valley is to cut off the head and boil it in vinegar. Nanny evidently struck lucky, geographically speaking. These days famed for the Outward Bound Centre in an old castle in the village of Notfaroute-on-Ah.