Heorot, Hrothgar's mead hall in Beowulf, was built to be the mightiest mead hall on all of the earth. It is through this hall's building that Hrothgar wished to honor God for all of his "glories in war...and honor in combat." Chapter five describes the hall, as Beowulf and his men walk toward it, as "bright with gold" and containing a light which "illuminated far off lands." The throne in Heorot was one which honored God (noted by the fact that Grendel could not approach it because of his exile from God's light).
Grendel,on the other hand, lives in a watery domain. Filled with sea-monsters and darkness, the lair is nothing like Heorot. While Heorot was built to praise God, the lair is a place God has forsaken. Given Grendel's ancestry to Cain, he is unable to live in the light of God. His domain is one of ogres, trolls, and darkness.