So I'm still exploring the mysterious tower east of Lofiathan, and at the suggestion of @smg34-shipper I went through the door with the big skull on it. (@hummingbird-hunter had suggested I stand in the middle of the big mystical symbol on the ground, but, uh, that seemed dangerous enough that I didn't really want to do it, though I did agree to go through with it if someone seconded the suggestion (or if no one else replied). Fortunately, no one did (and someone did). I mean, sure, a door with a big skull on it also seems like it could be dangerous, but these things are relative.)
Here's a map of where I've been so far on this level; I'm currently in the room on the upper right:
So it turns out that big skull on the door wasn't (necessarily) there to alert people of danger in this room. It was there because this is the skull room. The room where the owners of this tower keep their skulls.
(Well, not their own skulls; I assume they keep those in their heads. Then again, I haven't actually seen the owners of this tower yet, so who knows?)
This room is just... full of skulls. I mean, not haphazardly piled on the floor. They're arranged neatly on shelves. But still, there are a lot of them. I haven't made an exact count, but I'm pretty sure there are more than a hundred. Most of them look human, or at least humanoid (there are a few that look almost human, but maybe slightly off), but not all of them. I can see at least one horse skull, and one that I think is a giant rat skull, and one that I don't really know what it's a skull of—maybe a kangaroo, but that is a complete guess. I have not seen a kangaroo skull before, and am not completely sure what a kangaroo skull looks like, but it might look like this.
There are labels underneath most of the skulls, but they are in a language I don't know.
There is only one thing in the room besides the shelves full of skulls, and that is a desk. Sitting in a chair behind the desk is a skeleton. And when I say it's sitting in the chair, I don't mean like it's actually sitting up in the chair; I mean it's placed in the chair but it's slumped over the desk and not moving. I'd take this as an indication that this place is probably long abandoned and its original owners are long dead, except that I just saw the clearly recently used robes in the previous room, and even here it looks from the dust patterns like some of the skulls have been moved recently.
There's another door opposite the one I came in through. It's made of metal, and I can hear a crackling sound behind it. It's the same kind of crackling sound I heard behind the east door in the room where I entered this level, and in fact based on the map I'm thinking this door probably leads to the same room as that one.
So this time I've only got one obvious exit that leads me to somewhere I haven't already been, but I guess there are other things I can do. Any suggestions?
Go through the opposite door (with the crackling sound)
Take a closer look at one of the skulls
Try doing something with the skulls? (I don't know what I'd do with them, but I'm open to suggestions)
Look through the desk drawers
Investigate the skeleton sitting at the desk
Go back to the previous room (with the symbol and the cloaks and the tapestries)