For history & culture, Belém Tower delivers.
Up close it's a jewel-box of carved stone — twisted rope motifs, an armillary sphere, a rhino gargoyle. But the taste verdict most guidebooks won't give you: the inside is a let-down relative to the queue. The single spiral staircase makes the interior a single-file shuffle through near-empty rooms, and unless you're a Manueline-architecture buff the paid visit adds little. The real experience is free and outside — the riverside lawn, which is a tourist scrum at midday but genuinely lovely at early morning or golden hour when the light hits the limestone and the crowds thin. Photograph it, lie on the grass, skip the ticket unless the line is short.