A craftman of Dreams & Nightmares Quest (Divinity Original Sin 2)
Once you free Lord Arhu, he will tell you to seek Toyseller Sanders and he will help you get into the cathedral.
Go to the Toyseller's shop, and persuade him to help you. If you spoke to Arhu, you can tell him that Arhu sent him to help you get into the path of blood and he will agree to help you, giving you a source amulet.
He will also tell you to collect 'Scroll of Atonement' from above floor.
Both the source amulet and the scroll are needed to open the hatch in the Cathedral.
Arx Quests Playlist: https://www.youtube.com/playlist?list=PL_l3PEDN9zYhNSEWae6IUexF1FkaOCcCj
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