Once the Wishwall is complete in Hollow Knight: Silksong, you can start fulfilling side quests for the bugs in Bone Bottom. The first of these is "Garb of the Pilgrims," which asks you to collect twelve scraps of Pilgrim Garp.
In classic Metroidvania fashion, Silksong doesn't come out and tell you where you can find Pilgrim Garb. Luckily, getting the Pilgrims some (slightly) better vestments isn't that big of a hassle, and doing it nets you a very nice reward.
