I am a huge believer in ATMs, however, be prepared for the possibility that your magnetic stripe may cease to function. It's happened to me in Chile and in Spain. (This has happened to my credit cards, too, and even in Spain it was a problem, since most places can't--or won't--process transactions manually.) I'd recommend arriving in any country with about $100 in local currency; you never know what you'll find at the airport, and if you arrive on a holiday (I say this in general, not about Spain specifically), it can save you a lot of inconvenience, if not downright misery. When in transit, I always carry dollars in a money belt, and cards in my money belt and my purse. Once I arrive, I like to leave some of the above in a hotel safe, in case what I carry on my person gets stolen or ceases to function. Luckily, I've never been robbed. Technology, however, has failed me repeatedly.