The ancient Sith of Upekzar were known to have conducted their Mysteries' High Rites in an elaborate volcanic cave system, one of five such cave systems that together constituted the Circle of Visions. Like the other sites along the Circle of Visions, the High Rites cave system was home to both a colony of rhak-skuri, a subspecies of diplura whose pheromones were known to cause nightmare-like hallucinations in certain humanoid species, and an ancient Sith city located three kilometers away from the cave network.
The cave system in which the High Rites were conducted was a vast network of lava tubes and artificially hewn caverns located beneath a dormant volcano in a temperate region of Upekzar. Considered significant to the ancient Sith who first settled the Sith World of Upekzar, the High Rites site was eventually expanded to include a number of artificial caves where the Sith conducted their Mysteries' High Rites or prepared initiates for their ritualistic perambulations through the caves. One such cave explored by Natua Wan, Ben Skywalker, and Vestara Khai in 44 ABY still housed Sith lightsabers alongside scraps of decaying rugs and cushions. This cavern likewise bore a Sith language inscription on the wall that read, "Initiates, you who would master the dark side, prepare yourselves. Leave your weapons, and your former selves, here in this chamber—or depart now and forever in shame, before it is too late to turn back."
Like the four other sacred cave systems along the Circle of Visions, this cave system was home to a colony of rhak-skuri or "dream singers" in the Sith language. This subspecies of diplura hunted by means of a distinct pheromone known to cause nightmare-like hallucinations in certain humanoid species. The Sith who first explored and settled Upekzar developed a number of dark side rituals involving the use of the rhak-skuri pheromone that eventually turned the caves into nexes where the dark side flourished. By 44 ABY, the rhak-skuri endemic to the High Rites cave network had mutated into two-meter-high insects that possessed some degree of sentience, able to recognize and telepathically communicate with Sith and differentiate between light-sided and dark-sided Force users.
The caves in which the Sith conducted their Mysteries' High Rites was one of five sacred volcanic cave systems known to the ancient Sith of the old Sith Empire as the Circle of Visions. Unlike the sites that hosted the Rites of Fire and the Cold Rites, the High Rites caverns were frequented only by the strongest Sith Force users on the planet, most of whom lived a mere three kilometers away from the cave system in a city that dwelt in the shadow of a dormant volcano. Within the cave system, the Sith conducted the Mysteries' High Rites, a number of dark-sided rituals of Sith magic and initiations for Sith acolytes that made use of the caves' native inhabitants, the rhak-skuri. This insectoid species of diplura hunted by means of a pheromone known to cause nightmares and hallucinations in humanoid species. Over subsequent millennia, due to the residual dark side effects of the Sith rituals, the rhak-skuri mutated into two-meter-tall predators that freely stalked the caves.
In 44 ABY, during the Jedi Order's the search for Abeloth and Ship, Grand Master Luke Skywalker led a large Jedi strike team to the High Rites' cave system on Upekzar. While Skywalker and his Jedi searched the ruins of the ancient Sith city for signs of Ship, his son Ben Skywalker, fomer Sith Saber Vestara Khai, and Jedi Knight Natua Wan investigated the caves and encountered a group of mutated rhak-skuri. The creatures attempted to feed on Skywalker, ignoring Khai's attempts to distract them due to having recognized her as a Sith. Rather than lose Skywalker to the creatures, Khai sacrificed Wan to the rhak-skuri. As Abeloth sprang a trap that prompted the overhanging volcano out of its dormant state, the two surviving Force users were forced to beat a hasty retreat from the caves.