The following is what Malyarin knows about Purity from the reports of scouting missions sent into it from Tan'Shakar and the questioning of normal purity soldiers (not Knights of the Silver Flame - they don't talk).
Purity (not the worlds original name, although any other name has long been lost) is a huge hollow about twice the diameter of the Earth, but with the same surface gravity, apparently existing inside an infinity of rock. The sky is a pale silver-grey which gradually masks the landscape rising up on all sides. At the centre of the hollow space is a large very bright silver-white sun (about four times the diameter of Earth's sun) known as Bright Heart, which is orbited at close range by a tiny, very bright red companion known as Hearts Blood (about the only point of intense colour in the entirety of Purity). Because of the way things are arranged it never gets dark on Purity; people adjust their sleeping for the convenience of their lives and work. Purity has no oceans, only various rivers, lakes and small seas. The climate is generally hot and dry and varies very little from place to place (there are no seasons of any kind). The time rate of Purity is somewhat faster than that of Tan'Shakar.
The entire world has a silvery hue to it. Plants are silver with a hint of green; animals, although in shape similar to those of Earth, have silvery fur. The very rocks are silver, silver-grey or black. Gunpowder, electricity and explosives in general (including nuclear weapons and internal combustion engines) do not work on Purity. The architecture of Purity is based on a hexagonal floorplan (rather than the rectangular one used on Earth). The Knights of the Silver Flame say that as the world has approached perfection and total purity it has become more and more silver, though this has happened too slowly for anyone to notice a change within one lifetime.
The histories of the Knights of the Silver Flame tell how their faith was founded : thousands of years ago a woman whose name is lost, an exile from her tribe, was wandering alone in the wilderness when she stumbled across a great silver flame rising from the ground. She approached, entranced by Its beauty and purity, and the flame spoke to her. It told her that It was here to save the world by rendering it utterly pure, but It needed agents to carry out this holy mission. It had lured her here to serve as the first of these agents, and that if she had courage she could help to remake the world - all she had to do was step into the flame. Although afraid, the woman did so and was changed, stepping forth as the first Knight of the Silver Flame, and the first Keeper of the Flame.
The woman went forth across the world, gathering converts as she went. Those she found especially worthy were allowed to bathe in the silver flame and become Knights of the Silver Flame like herself; these were of both sexes and every one of them was (and is) an elite fanatic. They formed the officers and elite forces of the military forces of the Flame, commanding legions of normal soldiers. As time passed the influence of the followers of the Flame increased, and a city, which became known as Flameholm, grew up where the Flame rises from the ground. Eventually the first Keeper of the Flame died, and another keeper was chosen from among the Knights of the Silver Flame. In the time since then there have been many Keepers of the Flame, all of them female.
Some time after the founding of Flameholm the Flame began to flicker and grow weak. The Keeper of the time entered the Flame and communed with It. She was told that each time a Knight of the Silver Flame was created it drained a little of the Flames strength. Soon It would grow too weak to continue unless the Knights followed Its instructions. The Flame stated that in order to regain and sustain Its strength It must be fed with fresh human blood on a regular basis. The Knights obeyed without question, at first using the lowliest of the people under their control, then turning their eyes to people outside their nation as unrest grew. The Knights and their troops sallied forth, and soon took control of large areas of Purity, recalcitrant natives providing the blood the Flame needed.
As the power of the Knights of the Silver Flame increased, the remaining nations banded together to oppose them until there were only two nations - the followers of the Flame, and their (now nameless) opponents. Three hundred years ago the final war began. After decades of fighting the followers of the Flame destroyed their enemies and stood in sole control of Purity. They systematically destroyed the cultures and societies of the conquered nations, replacing them with their own.
Anyone on Purity can become a Knight of the Silver Flame if they can prove themselves worthy; there seems to be no correlation between becoming a knight and having ancestors who were Knights. However, the descendants of the first Knights of the Silver Flame (usually non-Knights) have become the nobility of Purity. They have divided the land into large estates, which they control absolutely. Above them are only the Knights, and the Keeper of the Flame herself.
The Flame has not spoken to the Keeper for hundreds of years. This is taken by the Knights as a sign that they are performing the Flames will to Its satisfaction.
The main temple of the Flame at Flameholm is a huge hexagonal amphitheatre which has been carved down into the ground around the Flame, leaving a hexagonal stepped pyramid in the centre from the top of which the Flame bursts forth. The amphitheatre is used as a viewing point for spectators of the various religious ceremonies carried out at the temple, such as when the Flame is fed the blood it needs. The temple is ornately carved with murals and abstract patterns (usually based on a flame motif) and is inlaid with a vast amount of precious metals and gems. Inside the temple-pyramid are carved the rooms of the Keeper of the Flame and her high-ranking priests, as well as guardrooms and rooms used for the various temple functions.
The level of technology on Purity has not advanced beyond a medieval level, in part due to the natural limitations on electricity and explosives on Purity, and in part because the Knights of the Silver Flame frown on any such dangerous innovations.
The opening of the Shadow Paths to Tan'Shakar six years ago came as a surprise to the Knights, especially when people from there came though, exploring and apparently wanting friendly contact. Even minimal contact with them convinced the Keeper of the Flame that these were dangerous heretical blasphemers who must be converted to the True Faith or destroyed. However, it would take time to assemble the forces needed to take their world. In the meantime the heretics must be lulled into believing there was no danger. This was done relatively easily, especially with aid of the Knights Flame-given powers. At last the armies were ready, and they marched along the Shadow Paths into Tan'Shakar...