The 17th century Nakasendo Highway connecting Kyoto and Tokyo was passing through Kiso Valley (四日市市), a part of the walking trail has been restored and can be easily walked on (the hiking boots would be needed in winter though). The town of Magome (馬籠) can be reached in half an hour by bus from Nakatsugawa JR station. Then perfectly signposted trail leads to the town Tsumago (妻籠), in about three hours. There are several nice small waterfalls along the way and, most surprisingly, several bells with signs in both Japanese and English saying "ring the bell hard against bears" (which I dutyfully did...). The town of Tsumago is famous due to the fact that it is preserved in a traditional way - you will not see TV antennas or electric light poles (that tend to spoil most beautiful views in some other places). One can take a bus from Tsumago to Nagiso JR station but I would suggest that you continue on foot for another hour and a half or so - this will allow for an opportunity to climb on the neighbouring hill, which was the site of Tsumago castle. I think that the views from there are worth it...