First of all, you must accept this quest from the unaccepted quests from the quest menu.
In order to do this quest, you must first arrive at current location: a peaceful and beautiful vineyard.
Then make the Giant dead grapevine track with the letter k and reach this point.
After climbing, you will reach current location: on the roof of the house, You see the beautiful vineyards below.
Item you need to buy: 1 straw_hat