The Museu do Piauí is the most useful indoor stop in the centre, especially when the heat outside becomes unreasonable. Its rooms cover state history, religious art, archaeology, natural history, and popular culture, with the slightly uneven character that provincial museums often have.
That unevenness is part of the charm. The museum gives context to a state many travellers only cross by bus: indigenous material, colonial religion, folk art, and political fragments all sit under one roof.