Joshua Schulman

I'm stuck in the Vahnati fortress North of Fort Remote. I've defeated all of the Shades, gotten Demon Slayer, and tried to find the lever to open the gate north of the stairs on the second floor, but I can't find it. I've been back to the Castle 3 or 4 times looking for help but I've got run out of ideas. This is really boring! Little help? Thanks