User blog comment:ProfDraco2/I! HAVE! RETURNED!/@comment-24588058-20171005193001/@comment-31772644-20171005221520

I'd say the original Eldunari wasn't a room proper, simply a series of openings where root tips became exposed. Warehouse 3 would have been the time they decided to experiment with Hephaestus' Anvil, which I imagine forges the energy of the smith into whatever they forge. So the sparks from that connect the energy of the Caretaker with the Tree of Idun, whos roots are spread all throughout the Warehouse, and these fires create the projections of the Nordic runes to represent the strength of their bond. Thus the weaker one of them is, the weaker the bond and if the fires go out, the Caretaker's connection with the Warehouse is severed.

Over multiple generations the Warehouse may have formed it's own room for the Eldunari, understanding the importance of keeping the "heart" safe, but I don't think it was like that originally. Nor do I think there's any connection to the Eldunari and the Restricted Records room. That's just a matter of convenience using the same door. Maybe something in that device can store doorways and impose them over another one?