And can be completed at level 7x, esp. if you're a Luminous (~35 hits of Spectral Light kills Castellan for mine)
Just pointing this out cause each level's under 1mil exp in that level range, so it levels you up once, and leaves you at 99.99% exp, if you loot the card. Which is basically 2 free levels for doing the Castle quests, but wastes a lot of the exp. Ideally, don't loot the full set until you're at 2+mil exp per level.