Look at the buildings around town. The hotels, the tourist information center, the police box, even the toilets have the same white walls and red roofs. This distinctive style is based on the ryokan, or traditional Japanese inns, that were built in this area during the late nineteenth and early twentieth centuries.
The buildings were designed to appeal to the turn-of-the-century European ideal of what a resort town was supposed to look like. On your screen is an image of the oldest ryokan in Unzen. The corridor was added to the original ryokan building to impress Westerners who were vacationing in Unzen during the same time period.