In 2293, the location of Remus in the Milky Way Galaxy was named in a star chart that was in Captain James T. Kirk's quarters aboard the USS Enterprise-A. (Star Trek VI: The Undiscovered Country, okudagram) The same chart was also visible in numerous places in the 24th century. (TNG: "Conspiracy", "The Measure Of A Man", "The Emissary", "The Mind's Eye", "The Game"; DS9: "In the Hands of the Prophets", "Cardassians")
Remus was tidally-locked, with one hemisphere always facing the Romulan sun while the other always faced away from it. The civilization of the Remans was located on the night side due to the extreme temperatures on the day side.
Political and historical
Remus and Romulus were the major worlds of the Romulan Star Empire. Remus was an important dilithium source and site of heavy weapons construction. Being forced to work in the dilithium mines, the Remans were regarded as an undesired caste in Romulan society but also had the reputation of being formidable warriors. In 2379, Shinzon, a Human clone imprisoned on Remus, became Praetor of the Romulan Star Empire by a coup d'état involving the murder of almost the entire Romulan Senate. However, subsequent plans that Shinzon had, namely to annihilate Earth, were thwarted by Starfleet Captain Jean-Luc Picard. (Star Trek Nemesis)
In Roman mythology, Remus and his brother Romulus were known as the brothers who founded the city of Rome. Remus was killed by his brother, who went on to become the city's first king. The relation between the planets of Remus and Romulus reflected this.
When it came time for scriptwriter John Logan to pitch his idea for a Star Trek film (which ultimately became Star Trek Nemesis) to Rick Berman, Logan initially spoke about revealing more of Remus than had been seen up to that point. Logan was inspired by the fact that the planet had never been fully shown on-screen before and that very little information had been established about it. (Star Trek Monthly issue 99, p. 31) However, Berman was at first baffled as to what Remus actually was, and precisely who lived there. "I said, 'The Remans! There's Romulus and there's Remus. We've never seen Remus; we've talked about it; we don't know what it is; let's use Remus,'" Logan recalled. (Star Trek: The Official Starships Collection, issue 31, p. 11) Eventually, the idea of depicting the planet won Berman's approval. "He loved that idea, once he knew what it was," Logan recalled, laughing. "So I'm really proud that I was able to go into the Trek mythology and add a part about what the Romulan Empire is." (Star Trek Monthly issue 99, p. 31) While Logan was writing the movie's script, the geography of Remus was one of many subjects he discussed with Berman, at what would have otherwise been an inopportune time, but for Berman making himself available to answer Logan's questions at literally any moment. Logan believed that learning about Remus in the film would be a long-due pay-off to Star Trek fans, owing to their curiosity regarding the planet. (Star Trek Nemesis (novel), pp. xviii & xxii)
In Star Trek Nemesis, the surface of Remus appears in only one scene. In the film's shooting script, the planet's surface was described as "a stark, desert planet with monolithic mountains and harsh crags shooting upward. The only light in this dark netherworld comes from the flames that accompany the hellish mining operations everywhere around us." This view was also described, in the script, as a "desolate vista." 
Remus appears in the film's opening titles. That footage of the planet was depicted with a CG planet model created by Digital Domain's Matt Fairclough, using a proprietary software system called Terragen. (Cinefex, issue 93, p. 90) Other establishing shots of Remus in the movie were achieved as digital matte paintings created by Illusion Arts, Inc., and included a view of the Reman mines. "We decided that we could do it in 2D rather than a 3D build, which would have been very expensive and labor-intensive," stated Syd Dutton of Illusion Arts. "Justin Brandstater produced a 2D matte painting that was projected onto 3D surfaces computer generated by Fumi Mashimo – just shapes to accommodate the painting. We split up the painting and over-painted the different surfaces; so as the camera moved through the shapes, it created a sense of perspective change. If we had built a CG model and then had to make changes, we would have had to rerender it or go in and change the texture maps. This way, all we had to do was touch it up in the painting." (Cinefex, issue 93, p. 102)
Illusion Arts was tasked with creating a second shot of Remus, which called for the camera to do a nodal tilt from the top to the bottom of a vertical mine shaft. To create that view, a unique approach was taken by Michael Kory and Mike Wassel. Taking advantage of the lack of parallax shift, they used a solution that combined 2D and 3D, in order to give the shot a photorealistic look, while also accommodating possible alterations far easier than a completely 3D approach would have allowed. Kory built, textured, lit and animated all the elements of the mine shaft in Maya, but rendered them reflected in an oddly shaped piece of geometry that resulted in a 360-degree view of the entire environment as a linearly reflected circular map. Next, Wassel painted atmosphere and lighting effects on the maps in Photoshop, and changed them into polar coordinate maps. These were then processed back in Maya, where they were simply mapped on a sphere, at the center of which was a camera. The tilt-down animation of this camera and render of the sphere supplied the final visual output that was used for the shot. (Cinefex, issue 93, pp. 102-103)
Remus was represented as one of two planets (the other being Romulus) in the Romulan crest, which was introduced in TNG: "The Neutral Zone". (Star Trek: The Next Generation Companion (3rd ed., p. 60)) The representation of Remus in the Romulan symbol was highlighted in a deleted scene from Star Trek Nemesis.
According to Star Trek: Star Charts (pp. 55 & 66) and Stellar Cartography: The Starfleet Reference Library ("Stellar Cartography", p. 17 & 34), Remus was a Q-class planet. The official name of the government was the Reman Colonies. The dominant species were the Romulans and Remans. Remus was in the Romulan War Theater of Operations (2156–60).