Here are a few spots to travel and explore for a day from mumbai. Alibaug 95kms away
Visapur fort trek
Durshet Powai lake is a picturesque spot of mumbai. Versova beach is the nearest to Powai, there you could gaze the sunset and sunrise.
- Matheran is actually quite beautiful. It's a tad less commercial than Lonavala or Khandala. - Alibaug is beautiful and you can take the boat/ferry there these days so you reach in about 1-1.5 hours. - Karjat has a theme park but I've never been there so can't tell ya anything about it. Also, there are some trekking trips orgaised by groups on weekends from Dadar. They have camping in Virar as well.