Hi Simone, Castellon is great small city. Close to the beach, fab central market, all the shopping you need and a train station. There's a good mix of older folks and families too. The city recently redid a lot of streets and sidewalks and hasn't suffered the flooding issues that the greater region has had.
We got a townhouse with a rooftop and the price wasn't bad, although I've noticed real estate is creeping up. For now we only stay for 2-3 weeks at a time as we both have jobs and older parents back in Oregon but that could change if things continue going poorly in the US.
Hope this info helps!