I had an idea after playing through "Halo" last month, of putting a new twist on the Earthmaster ruins. (Halo spoilers below):
The world of Kethria and its Earthmaster artifacts are not in fact modes of transportation, but the outer defenses of a prison, erected to contain the remnants of a deadly race of beings created by a god who was slain in the Natal Wars. The larval-state members of this race, known as the Flood, exist only to feed on others, and, by fusing with the corpses of those they swarm over and slay, can manipulate these bodies in a zombie-like fashion. Their incredible speed and ability to overwhelm all lifeforms made them an immense threat to those with whom they came in contact, and several nth dimensions fell before the Flood were stopped by an alliance of gods toward the end of the Natal War.
Judging that the only way of defeating the Flood was depriving it of food, an alliance of gods, along with their foot soldiers the Earthmasters, sealed the Flood within the nth dimensions they had already conquered. The gates themselves could not be destroyed, but they were "shifted" and twisted down to a single node: a Godstone located within the mountain stronghold of Larh-Darin on Kethira.
The Earthmasters, appointed to the task of containing the Flood, erected a series of Gates that served to capture and focus all attempts to exit the sealed nth dimensions and bounce them back to the prime gate in Larh-Darin. That gate is well hidden within the mountain complex, and protected by numerous seals of great power. Some have been pried from their settings in ages past and put to other uses by those who do not perceive their true function — the Sli-Hordrh, owned by Daelda the king of Evael, is one such artifact.
(The known functions of the Godstones are either features that allow the Earthmaster to quickly travel to a breech in the prison, or unintended but useful side-effects of their power.)
The Earthmasters remained on station for untold years, but eventually passed on. The seal on the prison remains strong, though the slowly failing power of the Godstone network may eventually threaten it. The few artifacts removed from the seal have also weakened it, but so few have been removed that the weakening is not yet perceptible.
The loosed artifacts have, however, led to mischief that may yet bring ruin upon Kelestia, for the Sli-Hordrh is not the only such artifact at large, and the Flood, though greatly reduced in numbers, are not yet destroyed.
In fact, the Flood. possessed of a hive mind, are in contact with a being they worship, and a being which regards them with favor. This being is known as Bukrai. Bukrai, unbeknownst to Morgoth (one of the gods who fought to destroy the Flood), has through its Shadow brought into being a secretive cult on Kethira, dedicated to destroying the seal (perhaps one of the 13 surviving founders of the Morgoth church was more deeply touched by Bukrai within the barrow of Urbrath). The members of this cult know nothing of the Flood, but are motivated by a desire to please their god, and by the knowledge of the artifacts to be won in doing so (some of the seal's artifacts are in the hands of the cult's senior members).
The cult is strongest in the Azeryan Empire, but has offshoots in Harn where many of the Godstones are (members, traditionally based in the chuch of Morgoth, also may be found within the church of Save-K'nor and the Shek-Pvar). It isn't a politically powerful cult. Focused more on the acquisition of knowledge, it is populated by sages and scholars, as well as able-bodied folk who can protect the secrets of the cult and brave the wilds. The cult's driving objective is to find Larh-Darin. Secondary goals include studying the Godstones and the acquisition of Earthmaster artifacts.
That's just a brainstorm. There would be more work involved in getting the above more in alignment with the info contained in various articles such as "Earthmasters." Fortunately, that article does suggest an ancient conflict the Earthmasters fought which nearly led to their defeat. The above might be tweaked in terms of timeline and details to bring into the mix Losenor, etc.
Extrapolating along these lines might liven up the Earthmaster ruins. Cult members certainly may be encountered in the ruins or centers of learning, though such encounters may not be deadly (is Lepridus of Telumar a member?). There may even be clues to the true nature of the ruins on their walls or in sealed rooms...