Well I was thinking that this skull represents some very very ancient race - maybe even divine who had some kind of cataclysmic battle with something potent enough that could turn somebody this big into stone. I leave it your fullest imaginations but I figured that this remaining skull would probably be on some outer plane and that millennia has passed by such that wind erosion has taken the sandy soil away revealing this skull which must be made of stouter stuff.

I'm guessing then that the area around this skull is barren and vast and that really there is nowhere to go once you exit. Theres really no reason to exit and no roads within miles and miles of it. Its probably barely known or else known only in some mythical sense like Noahs Ark would be now.

To my mind, if it were somewhere that you could get to more easily then it would have been fought over, made into some shrine and a city would have evolved around it. I can't imagine that anyone other than powerful wizards could fight over it and they don't need doors like normal folk do. Also, if a wizard had a lot of minions then maybe an abode which could house more minions would be different to this kind of place. A whole mountain, castle, island, or larger structure.

This is a retreat. A place to get away from other people.

I had a lich once who had his abode in a solid wall of dungeon disintegrated out. The only way in was a teleport and he had an emergency exit which was a thin tube where he could go gaseous form if required. I used to have things in my house rules where you got the teleport error in D&D but that you could craft some expensive and permanent items to a point and make that special teleport sites that removed the error. A sort of unique thing that was so familiar that it would not need the check.

In terms of scrying I reckon that he would indeed place protections over it. I would think that there would be some effect in place before any wizard cast anything that had something like that going on in order that this skull was never detected by the usual means. Perhaps it is the skull itself. Maybe the creature of this skull was naturally magic resistant to these weaker spells. Perhaps that is a good reason why the abode should be in the skull and not 100 yds to the north under the sand which would be less obtrusive... Maybe there are indeed lots more spaces in the rock surrounding this point which have bundles of books, pentagrams, alchemy labs etc.

Back to reality tho... My plan is to create top down 2D maps though I think it might necessitate making some 3D models to get a slice through them in order to figure out what the shape might be. How I get the arches and sinew shapes in to that I have no idea at this point. Maybe disintegrate does not work on the actual bone bit of the skull, thats why there is no door and the shapes will be defined inside. I was going to put a kind of window in the nasal bit - as shown on the sketch. Maybe thats the only way in.

Straw poll, what does everyone think ? If you were a wizard capable of going to this remote place and able to teleport would you think you still need a door ? I'm sure you might gather that I don't think it would need it.

I only started this cos my machine was chugging endlessly calculating terrain but its now turning into a bigger job... still, its always fun.