Dream-walkers, a group of Voss Mystics who were considered outsiders, engaged in the practice of Dream-walking. They weren't completely accepted by the Voss community and maintained a settlement within the caverns located underneath Voss-Ka, known as the Mind healer's grove.
In approximately 3640 BBY, the Sith Lord named Kallig sought out Asa-Ku, a dream-walker, in an attempt to gain knowledge regarding the Forbidden Ritual, a secret held exclusively by them.