While the onsen monkeys are outside on Monkey Mountain, the complex you are heading to is the indoor Hakodate Tropical Botanical Garden at Yunokawa Onsen. While the garden is nice, the undoubted stars of the show, especially in winter, are the Japanese macaque monkeys who soak in their own private onsen, often surrounded by snow.
If they're feeling enthused, you might get to see them jumping off their high wires into the onsen. If watching the monkeys gets you excited about getting into hot water too, don't forget that Yunokawa Onsen is a hot springs area and the nearby hotels will be happy to relieve you of your yen so you can have a bath too. To get here, take Hakodate Bus from outside Hakodate station for 20 minutes to the Nettai Shokubutsuen-mae stop.
