Pune is the nearest major city — 65 km and about 1 hour by road or train. It's a full city in its own right with museums, the old Peshwa-era town, Osho Ashram, and excellent food, and makes an easy and rewarding day out from Lonavala, or vice versa.
Rajmachi Fort, deeper in the Sahyadri, is a more demanding option: a full-day trek (or an overnight) that reaches a remote twin-peak Maratha fortification with outstanding views and a sense of real wilderness. The trek is typically done via Kondivade or Udhewadi village and takes 4–6 hours each way. Best in the monsoon for atmosphere, but the trail is a serious undertaking in rain.
Mumbai is 90 km away and about 2 hours by train or expressway. It is more logically a base from which to visit Lonavala than a day trip destination — making a full day trip to Mumbai from Lonavala and back in one day is possible but leaves little time. If you are based in Lonavala for a few days, a day in Mumbai is worth doing; if you are making a quick weekend trip from Mumbai, reversing the logic is more sensible.
