Hi Yash, I went to Pune for 4 days to enjoy monsoons of Western Ghat. Day 1: Visited Lonavala after resting the night in Pune and came back to Pune at night.
Day 2: Did Pune darshan
Day 3: Visited Mahabaleshwar and came back to Pune.
Day 4: Watched a movie in Pune and relaxed the entire day. You can go to Matheran from Lonavala or spend the night in Lonavala itself. You could also visit Lavasa one day.