Stamp 20 takes place in Fuji City. To complete it you must: go to the area in Fuji City with the red temple and there you'll meet a fortune teller. She is on the right side of the road. The Fortune Teller gives you 10 luck letters, it doesn't matter which luck you get. After you had a fortune told, the fortune teller gives you an interior. You simply go outside and earn a stamp.