How to add Santiago?
 

Thanks to help from everyone I have come up with the following itinerary for Spain in April:
Barcelona 5 nights
Madrid 5 nights (with day trips)
Sevilla 3 nights (with day trip to Cordoba)
Cadiz 1 night
Ronda/Pueblos Blancos 1 night
Granada 3 nights
Malaga 1 night (fly out from Malaga)
However, we have now decided that we would like to walk the Camino de Santiago for 1 week. Where would you add this to this itinerary? Fly to Santiago from Madrid and then back to Madrid and continue the itinerary from there? Or should I substitute some of Northern Spain or Portugal to this itinerary? We're open to changes. We generally like interesting places to walk around in, art, music, museums. We often rent vehicles but had thought to do this trip mostly by public transportation. I believe our international flights can originate or end in Madrid, Barcelona or Malaga. Thanks for any suggestions!

The walk starts near Pamplona in the French basque country, not in Santiago. I would do that from Barcelona.
That would mean dropping all of Andalusia--is that cool?

We are only planning to do just over the final 100 km of the walk so we would go to Santiago, take transportation to our starting point (We haven't chosen our route yet) and walk back to Santiago. We are planning to add a week of time so we don't really need to cut out Andalucia.

I have walked the last 100 Km, it's probably most convenient flying from either Barcelona (www.spanair.com) or Malaga (www.vueling.com) to Santiago, then take bus to Sarria.

I think that it's easiest to use Madrid to get to and from Santiago. Many of the flights between Santiago and Barcelona have connections in Madrid anyway. Santiago to Madrid is only 600 kms, to Barcelona well over 1,000.

Going first to Santiago before starting to walk has the advantage that you can leave your luggage in your hotel and just take a pack with a change of clothes, rain gear, and toiletries for the walk.

I am pretty sure there is a bus that goes directly from Santiago to Sarria, but I think it's infrequent. I know that you can go via Lugo (various trips each day), with a transfer to Sarria. You might check into leaving luggage at the Santiago airport, because you can get a bus to Lugo straight from there.

Buen camino!

A possibility would be to travel to Santiago from Madrid at the end of your days there and then to Barcelona from Santiago at the end of your walk. I believe there are also non stop flights between Santiago and Barcelona, on Spanair and Vueling. As lreynold says there is bus service between Santiago and Sarria (check www.monbus.es and see if it has that schedule). If money is no object I recently read that a taxi for up to 4 persons from Santiago to Sarria is about 90 euros.

Just found out that another possibility is to take the trenhotel (night train) from Madrid to Sarria, leaving Madrid at 22:30, arrival in Sarria at 6:50.

Thanks for your help!