We are taking the Rick Steves' tour of Spain in September. We are flying home from Madrid so we have one extra day there.
Would you go to El Escorial? If not, what would be better?
Looking at what else you won't have seen 'on tour' I think it's the best idea.
Avila and Aranjuez are a couple of other options.
If art is your thing then consider the Thyssen Bornemisza Museum or the Sorolla Museum.
Two other little gems are the convents - Descalzas Reales and Encarnacion.
http://www.patrimonionacional.es/real-sitio/monasterios/6095
http://www.patrimonionacional.es/real-sitio/monasterios/6144
I'm not sure where your tour will have been, but I'd suggest any of the following as a day trip from Madrid instead of El Escorial: Toledo, Segovia, Avila, Alcala de Henares. El Escorial is certainly worth a visit if you have time, but it appears you don't and I found all of my suggestions to be more enjopoyable.
Eureka I've got it ... the tour itinerary for Archimedes (above).
http://www.ricksteves.com/tours/spain-portugal/spain
Toledo and Segovia are featured days on tour.
If you plan on taking the AVE train from tour end in Sevilla to Madrid, then make sure you include a stop off in Cordoba on the way to visit the Mezquita.
If the Rick Steves tour does Toledo,I would go to El Escorial,we enjoyed it ,it is a very large place with the Royal Families burial place,lots of marble.
Mike
I had assumed it ended in Madrid, although you gave no indication that was the case. If the tour ends in Sevilla you have more options. I'd also consider a stop in Salamanca.