There is no such description. The Tomb of Sargeras Lore at Gamescom does state that the Temple of Elune was built on top of a wound that the Highborne sealed using the Pillars of Creation.
Considering the Chronicle mentions the Legion deciding to make the Temple into a Portal for the Legion it should be pretty obvious that whatever that wound was the Legion thought it could use it to open a second Portal into the Twisting Nether.
Not only did the Highborne of Suramar decide to seal the Portal but Queen Azshara’s actions in Azsuna using the Tidestone led to them sealing the Eye of Aman’Thul away alongside Suramar!
As for what the Titan Facility underneath the Temple of Elune was intended for: The Titans would never allow an Open Wound to go unprotected by the Pillars of Creation! The Well of Eternity was specifically converted into Arcane to seal another Azerite wound(which was threatening to destroy the planet due to the Azerite storm) so it is no surprise that the Titans would build a Facility to protect and research another Azerite Wound!
The Titans discovered that a wound in Azeroth could create a dangerous storm capable of destroying the Planet so naturally when another showed up they would secure and study it for research.
The Titans aside from Sargeras have zero experience in what World Souls are capable of handling(Argus survived having a gapping wound) so when Y’Shaarj’s demise caused a storm of Azerite to show up they decided to avoid harming anymore Old Gods and begin studying the mysterious substance under controlled conditions.
The Highborne for some reason or another sealed the Wound with the Pillars of Creation practically ending the Titans’ research on the mysterious substance whose existence keeps them from ripping out every Old God on Azeroth.
The Titans as the Brokers note merely make assumptions about reality and as Sylvanas stated that Azeroth was a prison not to mention the similarities between the names Azeroth and Zereth Mortis I would assume Azeroth is not a Titan but a prison for Death where the First Ones guard the Planet’s depths.
The function of Azerite? Keep visitors from digging deeper! Furthermore one of the Azerite Essences is called Anima of Life and Death which shows Death as being the Blue and Life(Spirit consumed by the Planet) as being the Golden.