Drura Sextus was a planet in or near Federation space, near the fringe of Klingon territory. Though largely mountainous and icy, it was classified as class M. In the 2360s, archaeologist Jennifer Almieri discovered Tholian artifacts on Drura Sextus, the first such discovery on an M-class planet. This discovery was used to support the theory that the Tholians had seeded the planets of the Alpha Quadrant millennia earlier, when those worlds were younger and hotter.
Among the discoveries on Drura Sextus were crystal-lattices with Tholian script, the first known examples of a written Tholian language. These writings described a race of genetically engineered shapeshifters which may have also existed on the planet.
At some point prior to 2377, Almieri and her team secretly abandoned the dig site on Drura Sextus, although they continued to claim to be working there. They relocated to a subterranean location, which may or may not have been on Drura Sextus as well. (CoE eBook: Ghost)