Against the cult: the Forest Ruin (1.5)

Ogbar steps into the room past the flailing arms of the dead priestess and, with one solid chop of his axe, breaks off the haft of the spear. Immediately the undead woman begins walking toward him, but then the barbarian grabs the end of the shaft and pushes it ahead of him, shoving the zombie backwards just out of its reach, east down the hall, back to the mezzanine and the railing above the drop to the first-floor pit.Albertus calls upon Pelor and he is filled with the righteous sense of any evil in the area. There is a strong sense of undead coming from the creature that Ogbar is pushing, and from the pit on the first floor. There are no other beings that he can detect, but he does sense an area of desecration above him...in roughly the same direction as the origin of the beams of light earlier (east and a bit south of where he is now)!

Xana and Kragga enter the room and look through it carefully, but everything else in the room is decayed and covered with a thick layer of dust. Whatever was in the desk - papers, or a journal? - has long since crumbled away.

Joseph, Theran, and Aanbo talk about traps. Speaking of traps, part of the spear shaft still extends out of a narrow hole in the wall in this bedroom. Anyone who isn't otherwise occupied can roll an INT check if they wish to examine it.

Following so that the barbarian will have light, Aanbo joins Ogbar at the railing, and awkwardly with one hand the dwarf holding the torch helps heft the broken spear (with the animated corpse skewered in the middle) up and over the top. Ogbar notes the gleam of the medallion around the priestess' slit neck as the corpse tries to reach him. Then the dwarf and human let go: the undead priestess falls and disappears through the floor below with a loud "CRUNCH!" noise. A moment later, another golden beam of energy emits from a patch of the ceiling a bit to the south, streaming down to disappear into the illusory floor below them.
Next to them, Albertus points to the ceiling to emphasize what he just said:
"Desecration right above us, friends!"

Joseph asks "What's this now?" but doesn't immediately see how the trap works/worked. Theran (who did so well with the traps outside), Xana, and Kragga remain in the room with him. Any of them could also try.What do you do now?

While Joseph traces the hacked-off butt of the spear into a concealed hole in the west wall, Theran surmises that there must be a trigger mechanism somewhere. He finds a button behind the door, positioned in the east wall so that, when the door is opened, the trap is triggered (presumably launching the spear out of the hole in the wall). But he also sees that there is a hinged "locking arm" on the button, connected to a rod going into the east wall. He calls Joseph's attention to it, and together they examine the southern wall of the corridor to the east of the door. Quickly they find that one of the stone bricks in the wall is loose; prying it out reveals a switch, and throwing that switch locks the button so that the trap wouldn't have been triggered when the door was opened.

There is a brief thudding noise from downstairs, then a bit of shuffling, then silence. Aanbo observes nothing emerging from the pit.
Joseph and Theran, knowing what to look for, are confident that can easily spot loose stones like that one again, and are determined to check for them before attempting to open any more doors (if they are in the vicinity, either one of them will automatically disarm such traps in future unless you request otherwise).
When the golden beams came, they seemed to pass through the solid stone of the ceiling as if it wasn't there, but Albertus sees no obvious way for people to go that way. But the stained stairway to the north leading up may be a route the party could take. There are also four unopened doors in the hallway that might also lead to other ways up.