Madrid to Andalusia train itinerary suggestions, in December?

Madrid-Granada-Seville-Madrid would be a nice loop by train. Spend the first night in Madrid, especially if arriving from overseas. Then take the train the next day. Spend 3 nights in Granada, 3 nights in Seville, then two more nights in Madrid before flying home.

It's easy by train, but rail service in and out of Granada is a bit sparse. Take a look at the schedule on renfe.com to see whether it works better for you to travel Madrid-Seville-Granada-Madrid or Madrid-Granada-Seville-Madrid. Most of the trains will go through Cordoba, so that city can be inserted anywhere that's convenient for you. It can also be treated as a day trip from Seville. That means an extra train leg back to Seville (and the extra train ticket isn't free, obviously), but you wouldn't have to change hotels or deal with luggage storage as would be necessary if you stopped in Cordoba on the way between two of your other cities. Cordoba is a lovely city and worth a couple of nights, but you don't have time for a long visit unless you're skipping Madrid on this trip.

Please clarify your dates: Is Dec 12 the date you arrive in Spain? Is Dec 21 the date you depart?

Seville is a lot larger than Granada and Cordoba, so it calls for more time.

Granada's not at sea level, so it will be a bit chillier in December than Seville or Cordoba.

Tickets for the Alhambra typically sell out way in advance, so that's something you should nail down early.

https://tickets.alhambra-patronato.es/en/ is the official ticket website. You want the Alhambra General ticket for a daytime visit. Some folks also like to see the Nasrid Palaces at night, but your time is short, so I'd recommend just the daytime visit. Figure on half a day or longer to see the entire (large) complex.

Less urgent will be the ticket to the Alcazar in Seville. Buy online in advance to avoid a usually very long outdoor ticket line, but the Alcazar doesn't typically sell out early.

There can be a long ticket line at the Seville Cathedral, too. Avoid it by buying a combo ticket at the church of El Salvador. This can be done on the day of your visit. Rick explains in his guidebook, which you should buy.

Thank you for the great ideas! Yes, arrive Spain on 12-Dec and depart 21-Dec - a great amount of time for immersion as well as exploration!

Thanks again @acraven and @travel4fun. What do you think of the following itinerary? We have been to Madrid before, so the emphasis is on the southern area.

12-Dec Fly into Madrid
13-Dec Train from Madrid to Granada
14-Dec Stay Granada
15-Dec Stay Granada (see the Alhambra)
16-Dec Train to Seville
17-Dec Stay Seville
18-Dec Day trip from Seville to Cordoba (see the Mezquita mosque)
19-Dec Train from Seville to Madrid
20-Dec Stay Madrid
21-Dec Fly out of Madrid

Gracias!

Seville is large, has a lot to see, and is new to you. One full day and a few hoursmisn't going to be enough time, so try to get there early from Granada and take a rather late train from Seville to Madrid.

Seville is large, has a lot to see, and is new to you. One full day and a few hoursmisn't going to be enough time, so try to get there early from Granada and take a rather late train from Seville to Madrid.

The Alhambra sells out early, so nail down that ticket as soon as you can. It's relatively inexpensive, so not a huge loss if the trip somehow gets postponed.

AI G,
If possible, consider spending your night of arrival in Córdoba, a beautiful city, then proceed on to Granada via train, or ALSA bus which may offer more time options than the train.
I definitely agree with acraven & also recommend more time in Sevilla. Since you’ve already visited Madrid, then consider staying only the night before your departure there and give at least an extra night to Sevilla.

Enjoy your trip!

Edited to add:
I forgot to mention. You may also take the ALSA BUS from Granada to Sevilla.
The bus station is on the outskirts of Granada so you’ll need to take a city bus, or taxi, to the city center. My mom & I took a taxi from/to bus station.

Thank you all! This has been super helpful. I now have my trusty Rick Steves guide too. Happy travels to us all!