The Sir Arthur Cotton Museum is a modest but useful stop at Dowleswaram, just south of Rajahmundry. Its subject is bigger than the building: the nineteenth-century anicut and later barrage that turned the Godavari delta into one of South India's great irrigated rice regions.
Pair it with a look at the Dowleswaram Barrage itself. The engineering is not glamorous, but it explains why the landscape around Rajahmundry is so green and densely farmed.