Spain will rearrange your mealtimes before it rearranges your map, and that is the part visitors underestimate. Lunch drifts toward two or three. Dinner starts at nine or ten. A plaza that looks abandoned at five is filling at eight. In smaller towns the afternoon pause is still real. In Madrid and Barcelona it has loosened, but kitchens still sit later than in Berlin or London. If you try to eat on a northern schedule you will wander through closed shutters and call the place sleepy.
The peninsula is a plateau with a hot centre and wetter, greener edges. Madrid to Seville on AVE is a couple of hours. Madrid to Barcelona is similar. Those trains are the reason a two-city trip is easy. Galicia, Asturias and the Basque Country are a different climate and a different kitchen, and they are not a side trip from a beach hotel in Alicante. Catalan, Basque and Galician appear on signs because they are used. Spanish will still get you served almost everywhere; English is concentrated where the tourism is.
The islands are a car problem
Mallorca, Menorca, Ibiza, Formentera, and the Canaries are Spain with a flight attached. Buses exist. They are not how you reach a cove or a mountain village on your own clock. Hiring locally, including from agencies that sit near the airport but are not the big multinational counter, is the usual way to make those islands work beyond the resort. Localrent is a catalogue of those smaller agencies, which matters when the international brands have emptied out for the weekend or priced a week like a deposit. You still need to park like the streets are older than the car. You do not need a hire car inside Barcelona or Madrid.
Summer on the meseta is harsh at midday. The Atlantic north can be grey in August. The islands in high season are a crowd plus a hire car plus a reservation for anywhere with a view. A week that holds is one region: Andalusia, Catalonia, the Basque coast, or one archipelago. The AVE will still be there if you come back.