In Harvest Moon: Back to Nature, the Aja Winery is managed by Duke and Manna. The Aja Winery is named after their daughter who ran away from home years ago. To get there, exit your farm through the front entrance (near your mailbox) and run past the Blacksmith. The Aja Winery is the next house on your left.
Here, you can buy Wine and Grape Juice from Manna. Other than that, there is nothing else here, with the exception of a couple locked doors on the second story. Perhaps if you become better friends with them, they might leave a few unlocked.
You hear machines rumbling and wine being made. There are shelves, stacked full with bottles of wine, though you may not drink any. Sometimes you can find Duke working in here.
Not very good friends with Cliff? Don't want him to leave? No worries! During the Fall, Duke will need help harvesting the grapes, and you can get a buddy to harvest them with you. Cliff is the only villager able to help, afterwards he'll stay for good. Don't want to lose profits from less grapes coming from you? No problem. Just run over Cliff using the run glitch, and get him stuck while you're ahead and you can harvest the grapes before him.