There is a script on this map that requires a very specific condition to activate that the player can accidentally render impossible to meet. The script must activate to allow further progress in the game.

In the room behind the Axe Door is a throne that four Chaos Serpents will teleport on to. The aforementioned script checks every few seconds that exactly three remain and lowers walls when the condition is met. However, it is possible for the player to reduce their number below three in those few seconds. In this case the script will never activate and the player will become permanently stuck.

If this should happen, use the "casper" cheat code and go through the walls on either side of the room, killing the Dark Bishops inside both hidden rooms. This will trigger the back wall to lower, revealing the second Heresiarch's lair. The Heresiarch may not be responsive, but attacking him will wake him up, and the game can proceed from there.