I will have a 11 hour layover in Madrid in May. What is the most affordable way to get into the city of Madrid? What is the quickest way?

the quickest way is taking a taxi - about 25 euros.
metro is cheap - but one has to make a couple of changes ( terminal 4 is not connected yet ).

Terminal 4 IS linked by the subway these days. I just did this trip in Feb 08. So, your most affordable way is take the subway (metro) to center of Madrid. It costs 2 euros each way and takes about 45-50 minutes.

Thanks YK and Danon! I wasn't for sure. I'm new at this "travel forum thing" and I posted this request twice (please forgive me). Thanks again!

Dear YK: If I was to use the metro what about the changes?

Depends on what you want to see in Madrid. Based on your screen name, I assume you would be interested to visit Prado? The "Big 3" museums in Madrid are quite close to one another.

Line 8 is the one that goes out to Madrid's Barajas airport. Prado's stop is Atocha station on Line 1. See Madrid's metro website for changes.
http://www.metromadrid.es/
http://www.metromadrid.es/acc_resour...Metro_2008.pdf

sorry, I was wrong about terminal 4 .
(we were in Madrid last year).
Where in Madrid would you like to end up?

I'm heading over to the Prado Museum. Thanks in advance for your help! Happy Travels!