The Nine Hells are not a place you can travel to outside the prologue to , unless you try to reach the devil Raphael's House of Hope in Avernus. This dungeon and mansion holds many secrets, and is where Raphael has enslaved other creatures and kept many contracts of infernal dealings. Legendary items can be stolen here, but only if you are willing to face one of the hardest bosses in the game.
The House of Hope can be reached by performing the Helsik Ritual in. One of the best things to do in Act 3 is to visit the NPC Helisk in the Devil's Fee shop, where you can buy the right items needed for the Ritual for around 20,000 Gold. A good Persuasion or Intimidation check can convince Helisk to lower this price to 10,000 Gold, but only if you promise to give them an artifact from the House.
The Helsik Ritual is a puzzle that involves placing five items in the right spots within a blood-stained circle. A special book handed over by Helisk after making another bargain details where each ritual object goes in a drawn pentagram.
Enacting the ritual will transport you to Avernus after creating a portal, and introduce you to the House of Hope's caretaker almost immediately. This NPC, Hope, has been magically enslaved and charmed to watch over this place for Raphael in. You'll have to pass a few dialogue checks with Hope to prevent her from calling upon the House's defenders to attack your party on the spot.
Gaining Hope's trust is crucial since she can give everyone in your party a disguise to let you travel around the House. This illusion transforms your group into debtors, or people who can not find a way to meet Raphael's devil contracts and are forced into servitude. This outfit gives you room to explore this hell-bound home to
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