I still cant find it
Im running around the 2nd catacombs (the one after the level where you have to open the 4 tombs to advance right) and I've gone to every tile I can find, the black squares. None of these did any sort of action when I ran the cursor over them or when my character himself walked over them.
Maybe I'm just at the wrong spot but I cant find any other black tiles through this level.
Yeah, you're in the wrong spot. Go back up to the first catacomb level (immediately below the caves) From the room that contains the ladder to the caves, exit north, then go west. There you will find two relatively small separate rooms in the big hall. They have, like, a cross of different coloured floor tiles in them. In the eastern room, the central tile of the cross wobbles ... as you can see when you move your cursor over it. You descend from there.
Coming to think of it, if you are coming back up from the 4 tomb level, it's the second room to the east of the stairs, you'll just have to skirt around the first room.
h.t.h. -Peter