A portion of the path is like a small maze that divides the crucible. From Zenetta walk back down the main road a short way and there will be a ramp on the left side. There are about 3 or 4 twists and turns to make before you come out on the other side. Then once you are back out on the street stay towards the left and the tower is a little ways up on the left side. It should be visible on your map once you are near it.
The tower has about 5 or 6 levels and you may want to bring help.
You need to find a way around the fallen roof. Luckily, there's a way through, just to the right of the debris.
Mr. Grimcaster is on the top floor of the Fleshless Tower. You can find his general location on your map. The sigil to get in is in the back of the tower.
