Temple of Darkness
The Temple of Darkness is some unknown ruined temple to the Charon (Lornon) pantheon that contained the same passage regarding Morgu (Marlu) as found in The Broken Lands. It was implicitly abandoned at the end of the Wars of Dominion, and alluded to conditions that did not exist until a few centuries after the death of Uthex Kathiasas. The way it portrayed several of the Dark Gods deviated significantly from their I.C.E. Age theology. It is not clear whether it is related to the Temple of Night which fell to the Loremasters in 450 Third Era, which might have been in Gaalt near the Wall of Darkness, and so may have been related to another surviving follower of Kadaena called the Master of Malice. "Morgu lyxatis kort" can be plausibly translated as "Morgu, Master of Malice."
Given the implied importance of Orgiana (Eorgina) in the underlying context of the Broken Lands, and her realm as the goddess of darkness, it is probable that the "Temple of Darkness" is supposed to be a ruined temple of hers. The Temple of Burning Night in southwest Jaiman was the center of her theocracy before she was banished to the Black Hel. It was run by V'rama Vair, the daughter of the Empress Kadaena. This would explain the poem venerating her as a "queen" when she was not actually queen of Charon.
Behind the Scenes
The Temple of Darkness is only mentioned in the poem that was released as one of the documents giving historical background for The Broken Lands. The Dark Gods were extra-planar beings who had arrived on the moon Charon, which was only the size of an asteroid, in 450 Second Era as an accidental consequence of dormant Lord of Essaence gateways interacting with the unnatural comet Sa'kain. The implication is that they were fashioned by the Empress Kadaena on a plane of existence parallel to the dark side of the moon and were somehow banished there at the end of the First Era.
While the ruins of the temple are implied to have been from the Wars of Dominion, the poem still refers to conditions that would not have made sense until the Third Era. Similarly, the same phrasing would have been used centuries earlier with respect to Morgu and its coupled stanza for Orgiana, which on face value is problematic. This may be rooted in "The Shadow out of Time" by H.P. Lovecraft as related to Kadaena being known as "the Shadow", which could go some way to explaining how The Dark Path was in homage of a goddess that died over a hundred thousand years earlier. (Though the idea of the sleeping demons telepathically imparting information, including prophetic visions, through the nightmares of unrelated cults is one of the motifs borrowed from "The Call of Cthulhu". The idea is also represented by the "shining trapezohedron" in "The Haunter of the Dark", represented by the crystal dome, which was "a window on all time and space" with the mind of Nyarlathotep.)
Consider: "The war gave me strange impressions of remembering some of its far-off consequences—as if I knew how it was coming out and could look back upon it in the light of future information. All such quasi-memories were attended with much pain, and with a feeling that some artificial psychological barrier was set against them." This is remarkable as The Broken Lands uses messaging of someone or something blocking against telepathy and teleportation. There is also room messaging that implies you feel like someone or something is watching you, which plays into the premise derived from the Great Race of Yith. One possibility is that Kadaena herself was dormant in the crystal dome which acquired power for her to resurrect as a goddess. Other servants became the Dark Lords. It might well be the point that they formed powerful non-corporeal entities (demons and dark gods) as avatars, and their death-like sleep amounted to transferring spirit or mind across time and space.