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