The world's largest outdoor laundry: a complex of over 700 open-air concrete washing pens where a community of washermen (dhobis) launders shirts, hospital linens, hotel bedding, and domestic washing by hand. The best view is from the pedestrian bridge on Dr. E Moses Road near Mahalaxmi station, where you can look down into the ghat without entering — the sight of hundreds of pens being worked simultaneously, with washing hanging to dry on lines above, is one of Mumbai's most memorable.
Guided tours of the ghat itself are possible with prior arrangement. Photography from the bridge is fine; photography inside the working area requires permission from the dhobis. The Mahalaxmi Temple nearby is worth combining with a visit.