Go in the opposite direction now (so right as you exit the initial door). You'll be able to see an Infernal Enchantress off in the distance. Head toward her and if you're not already in it, transition ...

Follow the corridor, going left, where you'll encounter a hound and snake-like enemy with a crossbow. At the end of this corridor, you'll want to go right and up the stairs. This will take you to a ...