Secret Seville ('Secret' guides)

Why is there a stone relief of Grace Kelly on the wall of Seville Town Hall and how can you track down the railway from the Ibero-American Expo of 1929? Where might you find the legacy of Christopher Columbus' son, a medieval Jewish cemetery in a car park, the oddest of barbershops, forgotten souvenirs from the Guadalquivir steamboats, Masonic symbols in a church, the last remaining vestiges of the Andalusian pavilions from the '29 Expo, a little known Modernist electric power station, an example of the Nazi Enigma machine, a collection of Chinese and Japanese art in a Renaissance mansion or the pillars of a medieval synagogue?