I believe that the elder halls of Gielinor are underneath........Draynor Manor! I can prove this by one obivous way, midpointing the Kra chambers.
Kras are statues, mouthpieces made by the elder gods over their respective egg, to talk to the Tokhaar for instructions without use of the Elder Horn. The Kra are located precisely over the egg chambers in the elder halls, so all we need to do is find their middle, presumably, the middle of the known world.
Jas in Ullek, so north west for him
Ful in Karamja, so North East
Wen between W.Wolf and Ice Mt. so South east slightly.
Bik is meant to be entrana, so north east
and finally, the blank Kra in Lummy,so north west
The midpoint between these spots is of course draynor manor, maybe this is why death's office is there, maybe the underworld is just the anima pool in the elder halls, where mortals are thinking that they are in the afterlife but will be consumed, this explains the Fremmeniks' belief that the DEAD FIGHT IN THE END OF THE WORLD! THEY ARE DEAD, but they are only dreaming that they are in valhalla.
There is my theory.
Peace.
