Lonavala, Mahabaleshwar, Lavasa, Khandala is best to travel in Monsoon. Full Rainy season and rainy days. Amazing Atmosphere and cool weather to travel.
From June starts monsoon season in Maharashtra. The weather moves from sultry heat to warm and then to chillness. There are downpours, sometimes cyclones and heavy rains. If you are a monsoon traveller this is an ideal time to visit Maharashtra, but your that days travel depends on that days weather.