Yesssss 1 day is too limited. I had about 4 days in Nagoya and still not done exploring!
Shirakawa-Go is in the UNESCO World Heritage site

it's one of the best place I've ever been. Definitely - the best season is Winter!!! In other times you can enjoy/ see different charm of the place, but without a doubt - Winter. Highly highly recommended.
Friends and I was there early Jan this year.
Day 1 - Shirakawa-Go. We arrived between 3-330pm and went out to play around 4pm after checking-in. It wasn't snowing. Whatever snow were there - a lot had been melted off by the locals to make it easy to walk.
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Day 2 Pic 1- Went out of the gassho-zukuri/ minshuku between 8-830am (as breakfast was served at 7am, also took some time to pack up) and there was thick fog. It was snowing slightly, but the night before there were heavy snow and we were so happy & amazed by the scene before our eyes.
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Day 2 Pic 2 - We stayed in the inner most part of ShirakawaGo village. Shirakawa-Go is huge and there are many different villages located in different parts of the 'mountain'/ area. Friend said this was the only place available as we did an adhoc trip, but I think we were lucky because it was so beautiful - beyond words. Staying at the innermost, although we had a long bus ride, was totally worth it.
We would see the mountain. And the snow were soft like cotton.
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Day 2 Pic 3 - We must check out by 10am, and by 10, non-staying guests/ tourists will start to flood the place (rule is that, no tourists or guests from other area can come in before 10am), they can only access the village from 10am-3pm. Times other than those are reserved for the village's guests. It was sad that we had to leave so soon, as the enjoyment felt so short. I'll definitely return one day. If you ask why so short, only 1 night - it's because you can only stay 1 night in gassho zukuri. All these places are usually overbooked so in order to ensure no one hogs the accommodation, everyone is only allowed 1 night stay - unless you move to another minshuku/ village for another night.
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Hope this inspires you to go one day

Gonna add Shirakawa-Go and Kiso Valley hike to my bucket list. In the meantime, gonna enjoy Nagoya/Kyoto/Osaka first this November.
LOL, Nagoya took me 2 years to exploring it. Within this 2 year, Every Sat & Sun took train / Bus from Tokyo to Nagoya to complete my research.
Perks of working in Japan. People like me just gonna visit Japan for a few days trip and back.
yeap sure, i will do it this weekends

Although google-ing adds to the enjoyment of planning a trip, having filtered/verified information or tips from other forumer make things easier. At least to me it feels more genuine coming from another forumer on a local forum. Benefited a lot from the 14 days Kansai itinerary in the 1st page by RegentCid.