Behind the waterfall there is a cave:
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After you got to the 255th floor of the middle class mines and got the sword of
legend from the princess, you can go to the cave behind the waterfall. To do this
you have to the sword equip, and then go to either rock by the waterfall and
examine it by pressing A. After the little cut scene is over and the has rock
have been destroyed, you can enter the cave. In the cave you will find a 12×9
field and like all in door areas, the time will have stopped.

Eligible girls:
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The girls that you can marry are: Harvest Goddess, Mermaid, Princess, Aafi, Arisa,
Erisu, Furen, Kaarii, Marivia, Muu, Nasuka, Reona, and Serena.

Field upgrades:
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The different items that you can use to upgrade your field houses will rot away
after different periods of time. The following materials can be used to upgrade:

Grass/ Hay: The weakest
Lumber: Average
Stone: Good
Golden Lumber: Excellent

Littering:
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The only place where you can litter is on your field. Anywhere else will cause
people to begin disliking you.