There’s a lighthouse in Cult of the Lamb’s Pilgrim’s Passage. Once you fuel up the lighthouse with wood to complete the Light in the Darkness quest, you’ll get a new quest — Refractions. The cultists in the lighthouse will ask you for 25 Crystals.
In this Cult of the Lamb Crystal guide, we’ll explain where to find those Crystals.
Each of Cult of the Lamb’s four regions give you a different resource. Darkwood is where you’ll gather Camellia flowers to heal your cultists, Anura gets you Menticide Mushroom Spores to brainwash them, Anchordeep is for Crystals, and Silk Cradle is where you’ll find Spider Silk.
On the far left side of the world selection screen, you’ll find the door to Anchordeep — the bishop Kallamar’s area. To get the door opened, you’ll need at least 9 followers.
Once you’ve hit that threshold, just approach the door to unlock it.
With the door to Anchordeep open, you just need to crusade for a bit. You’ll pick up Crystals like any other loot — especially from chests when you clear a room, but also from just destroying the environment.
Once you have 25 Crystals, head back to the lighthouse is Pilgrim’s Passage to receive a new follower form that looks like the head of the lighthouse cult (an axolotl, I think).