Just before we go on something about the pronunciation. Menu, pronounced the English way, is carta in Spanish. Here we're talking about menú, with the accent over the U. This word is pronounced something like menoo, the full phrase is menoo del dear, menú del día and it's a fixed price, set meal.
The menú is, generally, served in restaurants at lunchtime (2pm to 4pm) on working days from Monday to Friday. The price is fixed and it usually includes two savoury courses and then a pudding. It generally comes with a drink - water, wine, beer or pop - and bread. Spanish servers will be surprised if you order a tea or coffee to drink alongside your meal; hot drinks are for afterwards not during. Often, especially on the Mediterranean coast, you'll get a basic salad thrown in too. It's usually an either or between coffee and dessert though sometimes you get both as part of the package. Despite being so ubiquitous it's an unusual style of Spanish meal because each individual orders separately and eats separately. So often, when eating in Spain, the food is ordered to be shared.
There used to be legislation about menus but the Guardian article told me that was changed in 2010 so here are a few of the little tricks and ruses to look out for.
The most common trick, especially for tourists, is that they are drawn in by the fixed price menú advertised on a chalk board or similar outside the restaurant. Once seated the tourists are handed a carta, the a la carte menu. They're a bit unsure if they read the board correctly, it's difficult to ask and so they order from the menu and end up paying more. Usually it's a bit of a con. If you ask for the menú they'll tell you what it is though it may well not be written down anywhere except on that board outside. Sometimes the fact that they don't offer you a menú is not the restaurant being tricky. As I said most fixed meals are available at lunchtime on workdays. Britons often think of the principal meal as being the evening meal. If you turn out in the evening there is unlikely to be a fixed meal available but the advert for the lunchtime meal may still be there. The same at the weekends or on Bank Holidays.
Another of the standard tourist area dodges is to charge for things that are usually included - like the drinks, the bread or the salad. The server puts them on the table, you eat them and they turn up on the bill. If you read the the menú information it will be there; if the menú listing doesn't mention drinks (bebidas) or bread (pan) then expect to pay extra for them. Even when you know the extras are coming it can sometimes be a nasty surprise. We went in a place opposite the Sagrada Familia in Barcelona. We knew the drinks would be extra, we knew that it didn't include the coffee or pudding but it was still a good price for such a tourist mecca and the place looked nice enough. They charged me 6€ for a bottle of beer.
Most menus are not haute cuisine. A pal used to describe the menú choice as chop and chips. Plain and filling would be a kinder description though, every now and again, a menú can be surprisingly good. Even today, around here, there are, very occasionally, dead cheap but perfectly good menus available at around 7€. The majority are in the 9€ to 12€ range. There is often a second group of slightly better looking menus in some eateries - maybe 15€ to 18€. If the restaurant does offer a fixed menú on Saturday or Sunday expect the prices to be higher; the 12€ menú becoming 15€ and the 15€ menú becoming 20€. Obviously there are price differences with geography. If you're in Benalmadena or Benidorm then the food is likely to be cheaper than in Barcelona or Bilbao.
Still a good way to kill the couple of hours when the streets are deserted.