Why might the poet have chosen to provide such as detailed description of the setting of Beowulf's battle with Grendel's mother. How does this description influence the reader's impression of the battle

It happens in the depths of the lake that Beowulf dives into and then in the vault that Grendel's mother takes him to. It is clear that both the depths of the lake and the vault are described as very dangerous places that threaten Beowulf's life.