To start missions to access marapur you must:
"Go to the northeast area of Tiquanda and talk to Tarun. Ask about the asuri and he will tell you that sometimes the vile demons in the palace visit a far away place. He's curious about it but don't dare checking it himself, so he asks for your help."
For more spoiler please visit tibiawiki website and summer update 2022 page
Source:tibiawiki