The pool. Heated indoor pool and heated outdoor pool, according to the hotel's easyJet listing. Neither the temperature nor the period is specified.
I haven't yet found guest reviews that mention the water temperature. The easyJet listing also shows 4.5/5 from 4,867 reviews.
Guide's tip. With a covered pool on top of the outdoor one, it's a safe bet for swimming in spring and autumn. Get the outdoor pool's opening hours confirmed.