I noticed that in the thread that Xel made, the guide link is broken and old, so I made a new one that works with 4.0.3a .
For this, all you will need is a mount (big mounts work best) and slow fall or a buff with a similar effect. Its best to not be Gnome or Goblin, you might not make it through the wall.
1. This is the place on the map, get there how ever you can it shouldn't matter which way you take.
2. This is the entrance of the crypt, just go around the corner to the next step.
3. Stand in this corner mount up, as soon as the spell is almost done casting, jump and move forward. This wall is tricky to get through and it will take a few try's.
4. This part is also tricky. You must walk across the edge of that floor, to far to the right you'll fall on the stairs, to far to the left and you will be on the other side of the wall. Also once you start going across the floor will disappear and re appear (depends on the angle of the camera) be very care full, using the "/" key to walk slowly helps. Once you get to the other side, walk down on the little bit of land to the right.
5. Now that you are here and if you are a lock then put down a Demon Portal so if you make a mistake you can just port back. If you look back the way you came, there is more ground under the brick floor, just walk through them and DO NOT JUMP.
6. Stop here and make sure your feet is under ground.
7. For this part you will need slow fall or a buff that has the same effect, parachute works to, I had a friend who was a mage and he just buffed me and I was good to go. Being on the other side of the wall may effect the person giving you the buff.
8. Once you have the buff, you must run into the blankness you seen earlier and hope your feet don't hit the wall. Remember if you still have slow walk on, take it off or else it will be a short trip.
9. You should be able to see the first room of the crypt through that hole depending on the camera angle.
10. You should come right though this wall and TA DA you are there.
11. If you can't find anyone to help you if you don't have anything to make you slowly fall then don't fear I have recorded a video just for you .
12. Have fun exploring.