Look at the Google Map of Mumbai and you'll see a massive patch of green towards the northern suburbs of the city. This is Sanjay Gandhi National Park, one of the most visited parks in the world and home to over 1,000 plant species and 40 species of mammals, including leopards! There are so many things to do at SGNP that you should carve out at least five hours to explore it properly. You can walk the numerous trails, explore the 2,400 year-old Buddhist Kanheri caves, take a mini safari to see lions and tigers, and even paddle-boat.
The Bombay Natural Historical Society runs a lot of cool and cheap one-day programs, many of which are at the park. Check out their website in case you want to join a guided tour by the conservation society.
Meeting point: The park's ticket counter. Getting to the park is a journey but is fairly straightforward - catch a train on the Western railway line to Borivali station. From the station you can either walk or take a rickshaw to the park's main gate. Please note that it can take about half an hour to reach Borivali from Bandra and about an hour from Churchgate so plan accordingly to arrive at the main gate on time!
Leaders, the best time to visit is at dawn when the park is still cool from the night and quiet from the lack of loud school groups. The park is open from 7:30am to 6:30pm everyday.