Here is the full list of all 15 Lust for Darkness achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Spend 10 minutes at the cultists' orgy in the Yelvertons' Mansion
Finish the game
Rescue Amanda from the mansion
Complete the Side Story: Yelvertons' Legacy
Complete all the Side Stories
Complete the Side Story: Arcanes of Lusst'ghaa
Defeat Willard Yelverton
Complete the Side Story: Cult of Ecstasy
Go insane
Get captured by the cultists
Open the chest in Amanda's room
Listen to the full dialogue about the name "Lusst'ghaa"
Die
Enter the world of Lusst'ghaa
Enter the Yelvertons' Mansion