The maps show it in the wrong place, at least the Derida's map that I use do. If you port in from the inconnu crypt, go all the way to the top of the winding ramp. Find East track one, it will have Me'thya standing by it. Head east down east track one; about 1/2 way down, the ground dips away from the tracks, head south. Take the left fork, bearing east. Follow this around to the south. When you come to two barrels at a fork, take the right fork. Heading west now, you will come to a cavern, turn left, and head south about 20 paces. The door will be on your left, at loc 31.7, 28.8. Looking for it myself, I probably walked past it dozens of times, it blends into the left wall until you're right on top of it.