I cant remember the exact directions in Daryls tomb for the exp but it's the room before the one which leads you into the pool with the turtle (As in the one where the water level falls and you can enter the pool to pull a switch)

What you do is go down the stairs into this room and then keep going right and walk through the wall.

The Dream world is really confusing, a walkthrough is advised because if you miss any treasures you cant go back