The Winter Mine is a type of location in Harvest Moon: Back To Nature.
The Winter Mine is one of two mines in the game, the other being the Waterfall Mine. It is located at the Base of Mother's Hill, on the small island in the middle of the lake, and is only accessible when the lake freezes over in Winter.
Time stops while in the mine. There are 10 floors with a cave connected to the bottom floor containing an underground lake where the Catfish can be caught. The randomly generated floors are traversed by uncovering a hidden ladder using the Hoe. Ladders never appear on the outer rim tiles, and the hidden ladder will be in the area of the room diagonally opposite to the one you just climbed down. To exit, climb up the ladder on the current floor. Exiting will automatically send you outside the mine.
Two Power Berries can be found here. One is outside the mine, hidden around the back of the entrance. The other Power Berry can be randomly dug up on any of the 10 floors. The Ketchup Cooking Recipe can also be randomly dug up in the Winter Mine.