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There are five co-official languages recognized in the various regions of Spain: Castellano (everywhere), Aranese (Catalonia), Basque (Basque Country), Catalan (Catalonia), and Galician (Galicia).

In addition, there are several localized languages, that are not "official" but "recognized": Aragonese (Aragon), Asturian (Asturias), and Leonese (Castile and León).

And there are countless dialects of each.

For what is worth, Galician is essentially a variant of Portuguese, in the sense that it's mutually intelligible with European and Brazilian Portuguese. There are differences in pronunciation but not significantly more than between European and Brazilian Portuguese.

Castellano or Catalan, perhaps?

and also Basque (Euskara), Galego (Galician) and a maybe couple of other languages with a quite representative number of speakers.

They speak español.