Part of what defines Beowulf as a hero in this epic is that he is capable of superhuman feats. Before the episode with Grendel's mother, he offers a heroic boast to which Unferth takes issue, saying that it is not possible for Beowulf to have been able to hold his breath for long enough to fight sea monsters. However, in this episode (beginning at around line 1498), we see evidence that Beowulf does indeed have superhuman capabilities. The original Anglo-Saxon text says that Beowulf swims downwards "hwíl dæges" before he could even see the bottom. This translates roughly to "about the length of a day." So, Beowulf was swimming down to the cave for many hours—presumably the greater part of a daylight period rather than a twenty-four-hour period, as "dæges" in Anglo-Saxon more usually refers to the daylight hours than to what we might consider a whole day. Obviously, no human man would be able to swim for eight to twelve hours without running out of breath and drowning, so this is evidence that Beowulf is not like other men.

The exact amount of time is not specificed:

He leaped into the lake, would not wait for anyone's

Answer; the heaving water covered him

Over. For hours he sank through the waves;

At last he saw the mud of the bottom

It took Beowulf several hours or perhaps even more to reach Grendel. Deeds such as this one develop Beowulf as mythical hero, emphasizing his great strength, endurance, and resolve.