After the wine party, you can talk with Aryan again, to buy Yesem from him. After buying her, you can talk with her in your brothel near Aldlyn to get her solo CG scene.
25 days ago(+1)
Yes. The guide is at the bottom of the walkthrough pdf file, in the FAQ section for riddle solutions, or in the wiki at https://renryuu.miraheze.org/wiki/Riddles#Lum's_orpahanage_-_Dungeon_of_Cookie_a...
It's also possible to use a Riddle Key item to skip the entire area, if it's too frustrating.
25 days ago(+1)
My bad. I missed that image somehow during the upload. It's added to the wiki now.
The location is where the stone plates are on the other maps.