You will encounter various statues throughout the game and must turn them all to face a specific direction to get the Demon Orb. Then go to floor 5 to the room where the Golbargh demon is. This battle is very hard, recommend doing this on a non nightmare playthrough for your own sanity.
Statue locations and directions:
Floor - Location of the statue: (Direction to face)
Floor -2 - In the central room in the Lair of the Stalkers area (East)
Floor -1 - In the room next to the gambling den (East)
Floor 1 - Inside the Crypt area (South)
Floor 2 - In the open garden area just to the right of the Training Room (West)
Floor 3 - Statue near where you find the Demonomicon (West)
Floor 4 - In the room right next to the colored lever puzzle (East)
Floor 5 - In the room next to the bathroom (South)
Floor 6 - Northwestern area, in a small room (West)
Floor 7 - In a small room next to the Chicken Coop (South)
All credit to X-CalBR8 on GameFaqshttps://gamefaqs.gamespot.com/pc/284324-the-dungeon-of-naheu...