The Song of the Nibelungs (Nibelungenlied), the Middle Age poem based on germanic legends.
Sigfried, the hero, with his recently forged sword (Nothung), at the mouth of the cave where he meets the dragon (Fafner). He has been told that bathing in the dragon's blood will make him invulnerable. After slaying the dragon he baths in its blood... but a linden tree's leaf (upper right corner) fells on his back making him vulnerable at this single spot. Later this will be his ruin.