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