The 6th level of the Abyss holds the meanest room puzzle in Ultima IV. It is very difficult to solve this mess and many ways lead back to the beginning. Therefore here is a solution. The text is linked to the map of the problem, shown below it.
The first step is to find the illusionary wall in the northwest, which leads to the entrance leading to Room 1 (use the eastern door to enter it). Now walk south, through the Rooms 2 and 3, until you reach Room 4. Do not forget to dispatch of your foes on the way. Then walk east to Room 5 and then north to Room 6, before again walking east to reach Room 7.
In Room 7, dispatch your foes, before standing on the spot where the northeastern Balron had been, to open the south passage to Room 8. In Room 8, first kill all your foes, before walking on the spot where the eastern Balron had been. Have another companion then enter the illusionary wall east of where the southern Balron had been, to create the Bridge to Room 9. In the room walk south, to reach Room 10.
In Room 10, slaughter all the Headless with distance weapons, before leaving east to reach Room 11. Deal justice to the final wave of foes, before leaving either to the south or the east, to reach the altar.