Where does grendel die in Beowulf?

He dies in the sea-cave lair of his mother. The open wound of his armless shoulder leads the Danes and the Geats with Beowulf to the spot, but they do not actually see the body at that time. Only after the second attack on Heorot does Beowulf find Grendel's body, at which point (presumably not longer protected by his charms as in life) Beowulf cuts off Grendel's head and returns with it to Heorot.