In short
Mumbai concentrates Indian finance, cinema and publishing. Chhatrapati Shivaji station, Victorian Gothic from 1888, and the Elephanta caves out in the bay are World Heritage sites.
Colaba and Fort, in the south, carry the colonial architecture; Bandra and the northern districts hold contemporary life.
What it really costs
Mumbai has the highest rents in India, at a level that surprises: the south of the city rivals European capitals per square metre.
Suburban trains carry millions of people a day for a few rupees. They are the city's backbone and unusable at rush hour.
What nobody tells you
The monsoon, June to September, is intense: streets flood and trains stop. It is not a daily shower but a season that shuts the city down for days at a time.
Tours of Dharavi, one of Asia's largest informal settlements, exist and divide opinion. Some are run by residents and return their takings; others do not. The difference can be checked before booking.
The Elephanta caves need an hour by boat and close on Mondays. The last boat back leaves in the late afternoon, and missing it means sleeping on the island.