The Chamber of Candles was origionally a dark tunnel made by an evil king. He would throw his enemies into a deep pit dead or alive. Some have been known to escape. Husk later found the sealed tunnels and kept them secrect. The darkness and evil in the tunnels fueled his evil desires. He would cull the young there and throw them into the pit. During the battle against Husk, he escapes Crispin through the tunnels. When he sees a light at the end of the tunnel, he panics and notices the ghost-like figures of Urchin and Hope (Whom he assumes to be Prince Tumble) and stumbles back into the pit. His skeleton is found by Juniper, Urchin and Needle later in the seiries [The Heir to Mistmantle] when the veture down into the pit and find an escape route dug by animals who had escaped. After Husk's death, Brother Fir transformed the tunnels into the Chamber of Candles by filling them with light and love. They are mostly used for worship and prayer, but during the Raven War they are used as a place of refuge.
Before it became the chamber of candles, these tunnels were completely dark, cold and seemed to have ozzing slimy things spread across the walls and floor. It had a strange pull of evil and darkness to it.
After Brother Fir clensed it, the chamber of candles warm a dry. It's candles give a comforting glow.