Refuge is an achievement for Halo 3 and Halo: The Master Chief Collection. In the original game, it is worth 30 gamerpoints and is unlocked by beating The Ark on Normal, Heroic, or Legendary. In The Master Chief Collection it is only worth 10 gamerpoints, though it can also be unlocked on Easy.
In the original game it is represented by a blue plate with a roman numeral VI on it and also unlocks the EVA shoulder piece armor permutation.. In The Master Chief Collection it is represented by a screenshot of the level.
Note: You must complete the level completely through from Mission Start.