Lonavla Lake sits just outside town and is at its best in the monsoon and post-monsoon months, when the surrounding slopes are green and the water level is high. At that time it becomes a simple but pleasing picnic and viewpoint stop.
Do not build a whole itinerary around it in the dry season, when the lake can shrink and lose much of its charm. Treat it as part of the classic Lonavala circuit with Bhushi Dam, Tiger's Leap, and the hill viewpoints.