You appeared in a room with three portals - to the two remaining chapels and back to the Heresiarch’s Seminary. Get out in the open area and kill all the monsters there (mostly Centaurs and Slaughtaurs). If they bother you too much, you can also kill the Dark Bishops behind the bars in the chapel itself. Explore the whole area, you’ll see that it goes around one big building, the Wolf chapel. Amongst all the stone doors that cannot be opened (they open when a certain switch is pulled somewhere), you’ll find only one wooden door to be opened (it is in the south-western corner of the chapel). Go there and pull the switch inside.