Marine drive with Queens necklace of sodium lamps is the best place to spend time with your dear one. You can visit marine drive throughout the day and till midnight and its free of cost.
Accessibility is no issue, you can reach by local train, cab or bus or you can take bike ride at night.
Local sightseeing you can just seat and relax on the sea shore of marine drive, watching Arabian sea and feeling refreshing cool air. Nearby Tarapurwala aquarium, Wankhede cricket stadium, Girgaon beach, Nariman point just nearby.
Lots of hotels ranging from 3 star to 5 star properties for accommodation available along the roadside with reasonable charges.
Safety no issue at Marine lines because police personnel constantly present there. Beach guards are available near beach.
So I loved marine drive, whenever you visit Mumbai must go to marine drive.