Lilliana, had just another look there: No walls, just doors/levers, not even a secret wall. Please, have a look at the large map link I posted above: You can see there are doors, to the north and south of the exit room.
Kiya
Oh, how high is your gamma, please? Maybe you oversaw a lever?
Here is another large map of your level, click here, please. This map is from planetdivinity.
