Mahajanga's waterfront corniche is the city's best public room. It is not grand in a manicured sense; it is better than that, with food stalls, strolling families, traffic, benches, and the slow theatre of a port city turning toward evening.
Walk it late in the day rather than at noon. The light over the Mozambique Channel is beautiful, the snack stalls start to matter, and the city becomes much easier to read from the sea wall than from the hotter inland streets.