Don't forget that Spain is a member of the Schengen Zone, and if you are from outside the European Union, you will probably have a limit on how long you can stay. Americans, for example, can only stay in the zone for 90 days out of 180. That is, 90 days in the whole zone, not 90 days in each country. Read more about Countries in Europe that are in the Schengen Zone.
Here is my estimate of how long you should spend in each city in Spain. If you find you don't have enough time to see all the cities you wanted to see, leave some out and see them next time! Spain will always be here.
Of course, Spain is also great for a weekend break. Read more on Weekend Breaks in Spain.
- Barcelona Barcelona is a vacation in itself - you could spend at least a week in the Catalan capital just taking in the sights the city has to offer and then a second week seeing the countryside and towns around Barcelona.
- Madrid If you were to visit Madrid's three most important museums as well as the essential Madrid day trips, that'll take you nearly a week. Then there's my 100 Things to Do in Madrid.
Five DaysNot only are these cities two of the best in Spain, they each have a number of excellent day trips that should add a couple of days to your stay.
- Bilbao Bilbao has a number of great things to do and is also perfect for day trips to La Rioja, Santander and San Sebastian.