I worked for 6 weeks in Casa Balanza in Valencia washing dishes after my Leaving Cert in 1982 - about 50p per hour but all I could eat and I had free accommodation with a friend.
I never studied Spanish formally but picked up quite a lot in that time as no one in the restaurant spoke English- my grammar is poor and I learnt a lot of bad language.

However I loved my time there and have since gone back with my family.
As regards Castellano I can understand what people are saying and have a workable vocabulary. No good on Catalan or Valenciano
Sadly the restaurant is now gone as is its remarkable owner Enrique Grau. He also owned the Palaccio de la Belotta which I think is still going.