Rainy season in beginning of summer. Hot weather in the middle of summer. Typhoon season in autumn. Then, snowfall in winter. Pedestrian subway is not only for avoiding getting wet. You can also avoid the heat in the summer.
Pedestrian subways can be found near major railway stations throughout Japan, mostly in metropolitan area. One of the longest ones is located in west Shinjuku, Tokyo. It is 303 meters long and equipped with moving sidewalks.
One thing which you have to take care of when using the pedestrian subway is the exit. There are multiple exits and usually connected with buildings. Which means the you can not go directly outside without entering the building. Therefore do not get lost inside the building.