Here is the full list of all 12 Doorways: Holy Mountains of Flesh achievements.
Finish The Doorways Saga
Finish Act 3: The Temple
Find All the Notes in the Game
Find All Notes from Juan Torres
Find All Notes from Thomas Foster
Find All the Relics
Open the Gate to The Temple
Finish Act 2: The Mansion
Find All Notes from Celia Torres
Find All Constellations Notes
Finish Act 1: The School
Find your First Relic