From what I remember, the Death Realm is supposed to be vast, dark, and... strange. Part of the strangeness comes from weird shifts in gravity which happen from time to time or in certain areas. Personally, I think that would be really fun to have.
Perhaps having some tricky passages that take you in a loop if you go one way but not the other, though this would be trickier and potentially a bit too frustrating. Along the same strain, maybe having hallways that seem to extend on and on for one direction, but really don't? These wouldn't be lore, though, as I recall.
I'd like to see
layers to the Death Realm, too. Deeper, darker levels that you can get to, perhaps by making use of the weird gravity shifts or of stairways or ladders or portals and such.
Now, this is a bit more off topic but going to connect back to a layered Death Realm. A character can't enter the Death Realm for the first 15 hours, but what if there's some enthusiastic Dark Way mage wanting to join the Dark Circle, or some devout Dakkruist who wishes to gaze upon the Dark Crystal and read the scriptures in the Citadel's library?
Not at all sure how doable this would be, and as such it is solely a concept. What if when a character went to the Death Realm was not based on hours in game, but rather it was a percentage chance that increased every time they died?
There would be multiple spawn points in the Death Realm, perhaps one or two in each layer, and the upper layer(s) would be for those who have died either for the first time or barely at all. The upper layer(s) would be much closer to the exit(s), so that the souls newer to the Death Realm had a better chance of getting out.
The lower levels would be reserved for those who die more often, making it so that if you die more, you risk ending up in darker, deeper, likely more dangerous and stranger layers of the Death Realm. Perhaps each layer would get slightly larger going down, and there could be shortcuts one might be able to find to help get them to the exit faster.
Naturally the layers would only go so deep, and the lowest would be the bottom of the Death Realm. This bottom could have a slight variety of terrain, perhaps including a large lake of some dark, mayhaps dangerous liquid; a shoreline of this lake; some barren plains; and who knows what else?
Like I said, just a concept, and I don't expect this anytime soon.