In the course of his quest in Blood Omen Kain visited Avernus and it's Cathedral to challenge the Guardian of Dimension - Azimuth the Planar. Beforehand he was advised before by Ariel that he would have to "rise and fall and find [his] salvation in between" When Kain arrived in Avernus Cathedral he found it was apparently split into three 'realms', with teleporters linking them; these were seen as the Normal Cathedral; a bright white 'heavenly' realm; and dark 'hell' realm. The 'hell realm' was later revealed to be the Avernus Catacombs.