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