I’ve swum in pools at
- the albergue at Muruzabal (a wonderful place: the pool is just the icing on the cake)
- albergue Cuatro Cantones in Belorado
- the big modern Casa de Peregrino in El Acebo (also has a spa, but indoor and not so fancy)
- the modern Albergue at the edge of Barbadelo.
I also splurge on a spa hotel in Leon (hotel Q!H or Spa Paris) or Astorga (Hotel Spa Bia de la Playa) most times...a little more pricy but worth it as a treat.