I’m living right next door to Seville right now (moving away this month).
I loved both Seville and Cádiz, both of which have tons of things to see in the “old stuff” and “cultural” sections, Cádiz also has some gorgeous, long beaches of white sand; Tarifa is also nearby and if you like windsurfing it’s unmissable. Whether you’d like them or not depends on your own taste, but in any case I recomend visiting outside the summer months. If you like multitudes, that means come to Seville for Easter and to Cadiz for Mardi Gras (Carnavales); if you hate bein jogged, avoid those times. If you’re into natural parks, Doñana is “the” Spanish natural park, although I haven’t gone because it’s not my style (it’s mostly salt flats, I’m more of a mountains kind of girl).
And, well, I’m from Pamplona. You’re welcome to visit, either for Sanfermines (when the town does its best to become a 24h party for 8.5 days) or outside (when it’s a quiet, provincial little town with very good bars and restaurants and many museums and “old stuff” and “natural points of interest” either in town or nearby).