getting around in Spain

Train from Barcelona to Cordoba and on to Sevilla will be about 3 hours from Barcelona to Madrid, change trains (at the same station, Atocha), and then about 2 hours to Cordoba and 1/2 hour more to Sevilla (estimate, Sevilla is 2 /12 hours from Madrid.) Back track to Madrid to Atocha train station, and then take the train to Toledo, 1/2 hour. Back track to Madrid and take the Bus to Segovia, about 1 hour. It can be easily seen in a few hours The roman acqueduct (spelling?) the Cathedral, and the Alcazar. Backtrack to Madrid and take the train to Granada (I think) about 3 hours. Then to San Sebastian, by bus or Air...I have not made that journey, but did go to Santander on the coast about 4 hours by bus. According to the web site, the festival in Barcelona ends on the 24th. I would definitely cut out San Sebastian - a good place to visit, but not on the trip with these cities. You can stop in Cordoba for the afternoon, and even spend the night as you go to Sevilla Toledo merits an overnight stay inside the city if possible...Posada del Manolo is excellent as to location, price, and breakfast. If you plane to see the Alhambra (Granada) you must purchase tickets in advance on line. I would omit Segovia (a full day by the time you get there, see it and return) and San Sebastian on this trip (too far from the others.) Barcelona 3 nights Cordoba 1 night Sevilla 2 night Toledo 1 night Granada 2 nights Madrid 2 nights (not on your list, but you will be through it several times)
San Sebastian....if you want to go... That is 11 nights shown, allow for arrival and departure (2 nights) will be 13 nights. You may be able to see San Sebastian, but you are going to be very tired.....add a couple of nights along the way to other places.

HJ has provided some great counsel.

I'm all about options, so I hope you can follow my ideas. If you don't have flights settled yet, look to fly into Granada and home from Barcelona. This fits your schedule best. Arrive at Granada and stay three nights, seeing Alhambra on your second full day (first day to get oriented, take a nice walk, and recover from your flight/jet lag). 17 days isn't enough for a lot of additions to your itinerary so from there, train directly to Seville, stay a minimum of two nights (use your full day to see Cathedral, Alcazar, and Jewish quarter in that area) one evening can be a bull fight evening, the other can be to see a flamenco show. If you can add a day, Seville is a really good place to add. Take a high speed train to Cordoba early, get off for at least four full hours (1/2 day) to see the Mesquita and surrounding quarter, then continue by high speed rail to Toledo (you have to go into Madrid and change at the Attocha station). Plan two nights, one full day, in Toledo.

From Toledo, I'd opt (option A) for a bus to Segovia. I'm guessing it's the most efficient option (in time as well as money). Segovia has some nice sights, I can never get enough of medieval armor and the castle has a nice collection. I'd probably want two nights here also to give you a full day. If you're able to get there early, however, you could probably plan one night only. Another Segovia option (option B), if staying for two nights would be to rent a car in Toledo and make a short stop in Avila (great medieval walls) on the way. It's a little out of the way so I wouldn't try it if you only have one night in Segovia. With a rental car you could also make Segovia a day stop (option C) drive straight there from Toledo, see the sights from the Aquaduct to the Castle in a half day, then drive to Burgos for the night. Burgos would be a great place to stay two nights, they have some magnificent city gates and a great Cathedral. If nothing else take a quick look around in the morning, you will have made half your drive to San Sebastian (Donostia is the more local name) from Segovia. San Sebastian/Donostia is out of the way. A rental car or bus may be the best option compared to a train (with changes). I'd get a rental car to drop in Barcelona. Still, it's a five hour drive to Donostia from Segovia, so plan for a long day. If you do drive, plan to stop in Burgos for lunch and a quick look around. If you stopped overnight in Burgos it's about a three hour drive to Donostia.

Donostia is really nice when the weather is good. If, for some reason, you are expecting bad weather, it's probably a good place to skip. Otherwise, two nights here gives you a full day to explore plus two evenings to have some really nice seafood dinners (a caveat, Donostia is very expensive by Spanish standards). From Donostia, with a rental car, you can make a quick stop in Pamplona for a look around and/or stop in Olite (one of the best small castle visits I've found). If you choose both, I'd stop in Zaragosa for the night (a nice center for a short visit), then visit Montserrat on the way to Barcelona, drop your car closest to your lodging. Stay in Barcelona 3 nights. If Montserrat doesn't interest you, drop your car in Zaragosa and high speed rail into Barcelona. Or you can skip Pamplona, Olite and Montserrat, drive to Zaragosa, drop your rental, eat lunch, and train to Barcelona all in one day (it's too much if you make any stops). So it shapes out like this: Granada 3 nights Seville 2 nights Toledo 2 nights Segovia or Burgos 1 night
Donostia 2 nights Zaragosa 1 night Barcelona 3 nights So 15 nights, 17 if you add an extra night to both Seville and Burgos/Segovia. 4 nights in Barcelona isn't too much, so that's another option for an added night. One last note. If you drive, use the A roads rather than AP roads. The AP are toll roads and really don't get you there much faster than the A roads. N roads are also National roads but don't go as fast because they go through, rather than skirt, towns along the way (lower speed limits and stop lights). When using a GPS, choose the option to avoid toll roads (TomTom asks you each time, Garmin is in the settings).

i think you can do it and have fun. in october with 15 nights i visited san sebastian, bilbao, barcelona(for soccer match), sevilla, cordoba and ronda with the final night in madrid for flight out. i traveled by train solely. some long legs like bilbao to barcelona and barcelona to cordoba. but alot of high speed as well, like malaga to madrid. i liked cordoba almost more than sevilla, but granada kicks both of their, you know. barcelona reminds me more of paris with every visit but i am a gaudi nut. i arrived in madrid about 10am, 2pm train to san sebastian, arrived early evening, two nights, quick train to bilbao, two nights. long train to barcelona two nights, long train to cordoba two nights, super quick to sevilla two nights, quick to ronda one night, quick from ronda to malaga to madrid. toledo and segovia are quick from madrid, and madrid to barcelona on high speed is easy. possible night train from barcelona to granada. work back to cordoba and sevilla from granada. high speed to madrid then toledo and segovia. san sebastian in september should not be missed maybe day trip to bilbao the museum itself is pretty cool. have fun,be safe.