The armor itself can be found on the corpse of an assassin inside a secret room in Hag's End. While Hag's End can be accessed before accepting the quest, the pull chain to open the secret door will not appear until Olava has been visited.
Wearing this piece of armor grants the following skill bonuses:
- Resist Poison: 100 points
In addition, wearing the full Ancient Shrouded Armor set grants a 25-point armor bonus. It cannot be disenchanted.
This means the armor cannot be improved past flawless quality without boosting the Smithing skill over 100. This can be achieved by using enchanted items and/or blacksmithing potions to fortify Smithing.