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