For history & culture, Padrão dos Descobrimentos is hit or miss.
A striking, photogenic monument with a lift to a top viewing deck over the river and the giant compass-rose pavement plaza below. The honest catch: it's an Estado Novo dictatorship-era monument celebrating empire, so the framing sits uneasily with many visitors, and there's little inside beyond the view. Mostly a photo-and-viewpoint stop.