Spain! What a great country! You'll have a great trip!
I suggest your read the recommended itinerary from Rick Steves on this website:
(https://www.ricksteves.com/europe/spain/itinerary)
[Snippet below:]
By Rick Steves
So much to see, so little time. How to choose? To help you get started, I've listed my top picks for where to go in Spain, and outlined my plan for your best three-week trip.
Depending on the length of your trip, and taking geographic proximity into account, here are my recommended priorities:
3 days: Madrid and Toledo
6 days, add: Barcelona
10 days, add: Sevilla, Granada
13 days, add: Nerja, Ronda, Tangier (Morocco)
15 days, add: Salamanca, Segovia
17 days, add: Santiago de Compostela
21 days, add: Basque Region (San Sebastián and Bilbao)
25 days, add: Camino de Santiago (by car)