These are the dhobi ghats, the large laundry of Mumbai where thousands of people clean thousands of clothes everyday. A lot of people in India use this where these men (dhobi, a traditional laundryman) who collect, clean & iron the clothes in the place like this. These people live & work here. Later on it is continued by their next generation. If you get your laundry done in India, remember that it most probably goes to one such place.
