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