Then he girds himself for the new fight and follows the track of the second enemy across the fens.  Here is Hrothgar’s description of the place where live the monsters, “spirits of elsewhere,” as he calls them: 

                    They inhabit
    The dim land that gives shelter to the wolf,
    The windy headlands, perilous fen paths,
    Where, under mountain mist, the stream flows down
    And floods the ground.  Not far hence, but a mile,
    The mere stands, over which hang death-chill groves,
    A wood fast-rooted overshades the flood;
    There every night a ghastly miracle
    Is seen, fire in the water.  No man knows,
    Not the most wise, the bottom of that mere. 
    The firm-horned heath-stalker, the hart, when pressed,
    Wearied by hounds, and hunted from afar,
    Will rather die of thirst upon its bank
    Than bend his head to it.  It is unholy. 
    Dark to the clouds its yeasty waves mount up
    When wind stirs hateful tempest, till the air
    Grows dreary, and the heavens pour down tears.[9]

Beowulf plunges into the horrible place, while his companions wait for him oh the shore.  For a long time he sinks through the flood; then, as he reaches bottom, Grendel’s mother rushes out upon him and drags him into a cave, where sea monsters swarm at him from behind and gnash his armor with their tusks.  The edge of his sword is turned with the mighty blow he deals the merewif; but it harms not the monster.  Casting the weapon aside, he grips her and tries to hurl her down, while her claws and teeth clash upon his corslet but cannot penetrate the steel rings.  She throws her bulk upon him, crushes him down, draws a short sword and plunges it at him; but again his splendid byrnie saves him.  He is wearied now, and oppressed.  Suddenly, as his eye sweeps the cave, he catches sight of a magic sword, made by the giants long ago, too heavy for warriors to wield.  Struggling up he seizes the weapon, whirls it and brings down a crashing blow upon the monster’s neck.  It smashes through the ring bones; the merewif falls, and the fight is won.

The cave is full of treasures; but Beowulf heeds them not, for near him lies Grendel, dead from the wound received the previous night.  Again Beowulf swings the great sword and strikes off his enemy’s head; and lo, as the venomous blood touches the sword blade, the steel melts like ice before the fire, and only the hilt is left in Beowulf’s hand.  Taking the hilt and the head, the hero enters the ocean and mounts up to the shore.

Only his own faithful band were waiting there; for the Danes, seeing the ocean bubble with fresh blood, thought it was all over with the hero and had gone home.  And there they were, mourning in Heorot, when Beowulf returned with the monstrous head of Grendel carried on a spear shaft by four of his stoutest followers.