On a budget, Museo Arqueológico Nacional still earns its price.
€3 (free Sat afternoon & Sun)
A well-restored, underrated museum: the Iberian Lady of Elche bust and a replica of the Altamira cave ceiling are standouts, and it's rarely crowded. The catch is it's a comprehensive-history museum that can feel dry without interest in antiquity, and there's a lot of ground to cover.