In the 18th and 19th centuries, a roaring herring trade turned Esashi (江差; pop 8110) on the west coast of Hokkaido's southern peninsula, 70km west of Hakodate, into a boomtown. The Nakamura-ke Residence is the sole legacy of the town's glory days. The beautiful, sloping wooden house, made of cypress and stone (without a single nail) was built by a wealthy merchant; it's since been restored and opened to the public. Buses travel to Esashi from Hakodate (¥1880, 2¼ hours, five daily).
It's also well worth considering travelling here by car: the Oiwake Sōran Line (追分ソーランライン), which follows the undulating coastline, is a treat. In Esashi it's built on landfill: the Nakamura-ke Residence originally backed onto the water, so fishing boats could dock. There are some fantastic old photos of the town inside the house.