Comprising the neighborhoods of Dharavi, Matunga, Vadala, Sion, and Mahim, the northern boundary of this district is where the city ends and the suburbs start. But this distinction has been steadily blurring since 1945 when the city and suburbs were merged into an entity called "Greater Bombay" (The official preferred term is Brihanmumbai, which means the same thing.) The only remnant of this distinction is the fact that autorickshaws cannot enter the "city" limits.
This is a solidly middle-class district, which developed due to immigration after independence (in 1947). The Sindhis and Punjabis were refugees from the partition. They settled in Sion and parts of Matunga. Another prominent community to settle here were the South Indians, especially Tamils. They settled in Matunga and Vadala areas. The poorer migrants from Tamil Nadu settled in Dharavi, which was essentially a drained out swamp. So Dharavi turned into Asia's largest slum.
The district is not a tourist haunt, but if you want a slice of Chennai in the city, you could visit King's circle, Matunga and explore some of the bylanes. This is one rare district where the roads are actually walkable, as the footpaths in the Sion circle and King's circle area are well-maintained and free of hawkers and other encroachments.
This district is very well-connected with the rest of Mumbai. All three of Mumbai's local railway lines pass through this area. The Central railway stations are Sion and Matunga. The Western railway stations are Matunga Road (not to be confused with the Matunga station on the Central line) and Mahim. The Harbour line stations of Vadala, Guru Tegh Bahadur Nagar and Chunna Bhatti also lie in this region. In addition, the Western-Harbour link runs through this region and there has a stop at King's circle.
The Eastern express highway runs as far as Sion and runs into a perennial traffic jam at one point. Then it changes over to the Dr. Ambedkar road that runs all the way to South Mumbai. Road connectivity with the Central line is not that good. The roads exist, but are very crowded. BEST buses in the series 1-199 that serve South Mumbai also serve this area and are very frequent.
Cafe Coffee Day, Matunga. For the coffee lovers.