With Basque Country so close to Catalonia, Valencia, Spanish speaking municipalities, Portugal, and France; all of which have Latin influence on their language, why is Basque so different?
Basque was a pre-Indo-European language and evolved from Aquitanian, which means it was spoken in Spain before the Celts came to the Iberia and before the Romans did with their Latin.
We dont actually know Basque's relationship with other languages, we just know that it's unrelated to Indo-European (and therefore not related to Celtic or Latin, and by extension Spanish).
Interestingly two other pre-Indo-European languages were spoken in Iberia but we don't know enough about them to say they could have been related to Basque.