Here's what UNESCO has to say:
Located in a mountainous region that was cut off from the rest of the world for a long period of time, these villages with their Gassho-style houses subsisted on the cultivation of mulberry trees and the rearing of silkworms. The large houses with their steeply pitched thatched roofs are the only examples of their kind in Japan. Despite economic upheavals, the villages of Ogimachi, Ainokura and Suganuma are outstanding examples of a traditional way of life perfectly adapted to the environment and people's social and economic circumstances.
Basically, though, the houses are just darling. B and I both felt that the site got UNESCO status primarily because it was so cute. The setting is pretty beautiful too, though: the main village is surrounded by lovely mountains. The main point of access for visitors is on foot, crossing a long bridge spanning the nearby river.
|Bridge to Shirakawa-go|
|R and B on the bridge|
It had snowed heavily the day before, so we got to see the houses in their native element: their design is primarily a response to the winter conditions of the region, where snowfall can easily top 32 feet annually (or over 415 inches), with two meter high snowbanks developing. The snow may be a nuisance (Japan's government gives subsidies to areas with extremely heavy snowfall to help them with snow removal, etc.) but it also looks magical.
|Buddhist temple entryway covered in snow|
The houses are quite interesting architecturally. They were built primarily without nails, metal being too expensive, and are held together with rope lashings as seen in the picture below. As the area was a silk producing region, the houses are designed in multiple stories: the lower for living quarters, and the open upper stories for storage and silkworm areas (the rising heat would provide the high temperatures silkworms need to thrive).
|One of the gassho-zukuri houses|
|Closeup of the thatched roof: it's easily two feet thick|