How many days you choose to spend in Spain will largely depend on where you're going and what you want to do when you're there. For example 3-5 days would be enough time to see the highlights of one of the most popular city destinations like Barcelona or Madrid. However, with a week or more, you'll be able to explore more of the city and perhaps multiple regions. If you're planning a relaxing beach holiday, a popular amount of time is 8+ days.