Here is the full list of all 39 Cathedral achievements.
Acquire all Ouroboros amulets
Die one hundred times
Have more than 50 000 gold stored in the bank
Complete the game without upgrading the armor
Find all map pieces
Acquire all health bottles
Return 100 books
Find all armor augmentations
Find all ammo upgrades for the Flintlock
Kill Ardur
Kill 150 skulls (of any kind)
Find all ammo upgrades for the Magnus Apparatus
Destroy the Conduit
Find and activate all portals
Kill the blood knot
Kill Oloc
Have more than 25 000 gold stored in the bank
Return 80 books
Find all hearts
Return 60 books
Return 40 books
Return 20 books
Kill Nidlong
Kill 150 blobs (of any kind)
Find all charms
Slay all gargoyles
Buy the Onyx armor
Kill Thalia
Buy the Tourmaline armor
Kill Salemacke
Kill 100 skulls (of any kind)
Have more than 10 000 gold stored in the bank
Kill the Necromancer
Destroy an electric orb in Necromancer's den using the lantern
Kill 50 skulls (of any kind)
Kill 100 blobs (of any kind)
Buy the Emerald armor
Kill Augr
Kill 50 blobs (of any kind)