Shivaji: Hindu King in Islamic India by James Laine (2003) — A short, scholarly biography of the Maratha king whose forts (Lohagad, Visapur, Rajmachi) dot the hills around Lonavala. Laine places Shivaji in his full historical context, arguing against both nationalist hagiography and dismissive colonial accounts. A good read before climbing a Maratha fortification.
The Wonder That Was India by A. L. Basham (1954) — A comprehensive survey of the civilisation of the Indian subcontinent before the arrival of Islam, with extended sections on Buddhist art, architecture, and monasticism. The chapters on rock-cut architecture and early Buddhist patronage give real depth to a visit to Karla and Bhaja — you'll understand what you're looking at, not just admire it.
The Saga of the Indian Railways by Rajendra B. Aklekar (2012) — A popular history of Indian railways, with substantial coverage of the Bombay–Pune line and the engineering feat of the Bhor Ghat incline. The Central Railway route that serves Lonavala was one of the great 19th-century engineering projects; understanding how it was built makes the train journey through the ghats more interesting.
Sacred Waters: A Pilgrimage up the Ganges by Stephen Alter (2001) — Alter's writing on the Himalayan foothills and river geography is the best literary introduction to landscape travel in India. While not set in Maharashtra, his attention to how landscape shapes culture and memory is directly applicable to the Western Ghats and the way Mumbai and Pune use Lonavala as a seasonal escape valve.