Banos in Spain

You will find "aseos" or "servicios" in museums and historical sites with paid entry, such as the Alcazar in Sevilla and Alhambra in Granada. At the Alhambra, the clean and spacious restrooms are outside the ticketed areas, so available any time. In Seville I remember a modular style pay toilet (1 euro, I think) in the park by Plaza Espana. I do not remember seeing other public toilets around but they may be there. And there are public restrooms in the department store El Corte Ingles. The one in Barcelona, by Placa Catalunya, is well worth a visit, especially if you want to buy saffron, Spanish paprika, or other specialty items as gifts or souvenirs. We didn't shop in Sevilla or Granada, but they have this store as well. As for hotels, choose a large, upscale, impersonal one, and walk in like you belong there and know where you are going. I don't like to try restaurant facilities unless I am actually dining there. (Note: we ate twice at Bar Olivar in Granada and it was great. My husband said the restrooms were amazing, but I didn't go inside to see.)

Lola covered it very well, all I can add is that a few times we did ask to use the restroom at a bar or restaurant when we weren't eating there, and they were agreeable. If you feel uncomfortable about it, buy a bottled water or something. Be sure to have plenty of tissues/panuelos with you at all times. Many of the women's restrooms that I encountered did not have toilet paper, even in some museums/tourist attractions, especially later in the day. Almost every restroom had an automatic air-dryer for hands which generally didn't work so you may want something for drying your hands as well.

We live in Spain and it is quite common for people to come into a bar/cafeteria from the street, just use the bathroom and leave. It seems (at least in Andalucia) to be quite a normal occurence and something the owners are not bothered by. We regularly see people who are unfamiliar with that bar/cafe come in and ask where the bathrooms are and in all cases directions have helpfully been given. They will generally have signs 'aseos' or 'servicios' , usually one for women (senoras) and one for men (caballeros) or a sign with woman or man. Only very occasionally have I seen a sign which says they are for customer use only but if in doubt, grab a coffee or a water. I would go for bars/cafeteria places rather than restaurants or hotels. Yes the cleanliness, and paper supply, can be very variable and often the complete opposite of what you would expect - scruffy bar/pristine loo and vice versa.

We did as Rick Steves suggested: There are Starbucks, McDonalds, Subways, etc. everywhere in Spain. When in need, use their facilities. We were not questioned or stopped once. Buy a coffee or water if it makes you feel better - we chose ice cream cones!