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