Here are some of the beaches to be definitely visited in mumbai.

1) Aksa beach:
This beach is known for its quietness , calmness , beauty and serenity.  It is not advisable to stay there after 7 in the evening for safety concerns. One can reach this place by bus from malad station on western railway

2) Dadar chowpatty:
Dadar chowpatty is suitable for long walks , jogging and having snacks at various stalls over there. View of the bandra worli sea link with the sunset is unique to watch.

3)Girgaum chowpatty:
Known as the most famous beach after juhu, this place is always crowded with people. The food stalls here sell amazing street food like pav bhaji , masala pav , biryani, pani puri  and ragada pattice.This beach is relatively smaller but has many important landmarks around it.

4)Gorai :
This beach should be visited before dark because of issues of high tide. It is yet to be developed as a tourist spot and acts as a connecting junction to go to manori and the famous essel world and water kingdom. You can reach gorai by ferry from malad or borivali.

5)Juhu:
It is the longest beach in mumbai spreading upto  six kilometers. The food stalls here are a must visit because people over parts of north India , west , east and the south sell their regional foodstuffs introducing  us  to a variety of food specialities of different regions.Actor Amitabh Bachan's bungalow is not too far away.

6)Kalamb beach:
It is located in nallasopara , a station on the western line after Vasai .Lazing around is the favourite activity here.

7)Madh island:
Located in malad , it comes after aksa village. Take direct buses that goes upto madh island.

8) Marve beach:
Marve is comparatively smaller and narrower than other beaches because of its quick Sand. It became famous for its picnic spots.

9) Uran beach:
It falls between Panvel and Karjat and is far away from the city side. One can see remains of Karanja fort.

10) Versova beach:
It is an extension of Juhu beach towards Andheri. It is connected to versova village fish markets which are very famous. Lot of crowds have been seen here during Ganpati visarjan.