If starting from https://www.sanskritimagazine.com/little-known-history-of-goa-and-the-portuguese-inquistion/ and working farther into the past is acceptable. A fair bit to the south of the gangetic region.

Also, depending on your end goals, which are difficult if not impossible to discern from your post as of this writing, you might want to find out the background of the authors of the book. Most stories about India as is known outside India is narrated and steadfastly owned by non Indian voices. So if you are looking to work in a think-tank for instance, you'd steer towards authors who advocate German speaking region's interests with regards to India. Or if you are looking to work in diplomatic capacities, the authors might be of that leaning.

Bear in mind the current government's push to own the narrative to the exclusion of outside voices. Totally understandable, whilst being something to be mindful of.

Regarding religion. Doubtful of getting anywhere without running into religion as far as India goes. The science vs religion dichotomy works differently outside of the West, for all I can see.

The India of Mahabharat era encompasses today's Afghanistan, for what it's worth. Going by Indian archaeologists -- https://www.booksfact.com/history/ancient-gandhara-kingdom-kandahar-afghanistan.html

Also, another decent starting point would be, Constantino Giuseppe Beschi. The man who most recently resuscitated the then dying language of Tamil and led to original Christian literature being written in it. Tamil, along with Sanskrit is listed as a classical language by UNESCO IIRC.

What Odin said to Thor. Asgard is not a place, never was, never will be. It is the people.

That second worse city in the world is Delhi India for those wondering.