I have been to Yunessun a few times, and it's always a TON of fun! There are so many different themed baths there, and the best part is that you can enjoy the hot springs with your mixed gender friends since you wear your swimsuit here.
Like other onsen entertainment places, you receive a waterproof bracelet to use to pay for everything inside the park, which is great because there are snack vendors offering hot sweet potatos, green tea ice cream, and other yummy snacks. You can also get massages here, but if you're cramped for time I wouldn't bother. Yunessun definitely requires a full day trip to really enjoy the place. It's worth checking out if you plan to be in Hakone. T
Just remember...if you have tatoos you should either wear body makeup or a swimsuit that covers up your art.
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