Which language, spoken by about 8,000 people in northern Spain (Navarra), is considered a 'linguistic isolate', that is, not genetically related to any other known language in the world?

Basque (or Basque) is the last survivor of the languages that were spoken in Europe before the arrival of the Indo-European languages. Its origin remains a mystery to linguists, and its grammatical structure and vocabulary are not related to any other living language, making it a true linguistic fossil.