Goa: A Traveller's Historical and Architectural Guide by Anthony Hutt and Lacerda Dias — a methodical but rewarding survey of Goa's Portuguese-era buildings, churches, and mansions. Useful for anyone who wants to understand why the Church of Our Lady of Mercy looks the way it does, and how it fits into the broader colonial architecture of the territory.
The Goa Inquisition by A.K. Priolkar — a documented account of the Portuguese Inquisition as it operated in Goa from 1560 to 1812. Not light reading, but it places the churches and the legacy of Portuguese rule in an unflinching context that the tourist literature tends to avoid.
Goa: A Daughter's Story by Maria Aurora Couto — a memoir and social history by a Goan writer tracing her family's experience through the Portuguese period, Liberation in 1961, and the decades since. One of the best accounts of what it meant to grow up in a Goa caught between cultures.
When Asia Was the World by Stewart Gordon — not a Goa book per se, but one chapter follows Moroccan traveller Ibn Battuta's 14th-century journey through India and the Indian Ocean world, with passages relevant to the Konkan coast that Goa sits on. Puts the place in a longer frame of trade, religion, and movement.