Grendel is living in a place we can refer to as
hell (metaphorical), the place is inside mountains, a kind of cave with intense
smell and waste, which produces an impression of Grendel as a vicious and
insensitive entity.
As the origin of Gredel is tracked back to Cain who killed Abel
that is also adding up to the description of him being vicious, selfish and
insensitive monster.
