Talk to Munne to get the Votive Candles then descend into the Catacombs and head to the left (the same area you have to go for A Monk's Mission). Each candle must be placed on a brazier that has a Restless Spirit protecting it. The Restless Spirit should take out most of the monsters in the area if you hang back and wait. The floor in this area is flooded with diseased water, so move quickly, and rest on the dais at the other end of the maze area to regenerate your health.