Hey, Pune has alot of place nearby to drive solo apart from Panchgani/Mahabaleswar, let the rains start and the options will will open up alla round.
1. During the monsoons the drives on the Pune Mumbai highway itself is extremely beautiful.
2. Drive to mulshi dam is also beautiful.
3. 3rd option is Malshej Ghat, it's against beautiful drive during monsoons.
4. Bhaja caves, bhedse cave, Bhatala caves are also beautiful options.(nearby lonavla)
5. You can opt to check out singhgad, lohagarh fort, purandar fort, rajmachi fort if interested for little hike along with the drive.
6. The Bhuleshwar temple on the Sholapur route is also a beautiful destination.
Inthe late monsoons you can visit Satara Kaas plateau to enjoy the flowering .
7. tamhini ghat is another beautiful road to explore. And this road to lead you to the Konkan area, which again has an entire road trip to explore the beaches.
8.Lavasa is also a option, the drive is beautiful and you can enjoy beautiful sunset and sunrise, but apart from that I didn't like the place much.