Oblivion - I was in one of the Alyeid ruins, spelunking into its depths. This one ruin had the lovely floor trap which would thrust you up into the awaiting spikes, yet that wasn't involved in the glitch.
Further in, I heard the distinct sound of a land Druegh, so I unsheathed my sword and prepared a restoration spell. Looking about, I couldn't actually see it, and yet my detect life enchantment clearly showed it behind one of the walls, at least five feet from the floor. Dumbfounded, I blankly stared at the shadow dancing along the wall, and then, without warning "KYEEERAAAHHH!!" the land Druegh comes screamin' out of the wall like a bat out of hell, its claws tearing at my face.
The kicker is that this continues to happen, nearly every time I enter an Alyeid ruin with a land Dreugh in it, it gets stuck, and then engages in surprise ass sex whenever I have my back to the wall...