Ideas for three week itinerary to Spain

The subject of side-trips in Spain has come up frequently in recent months. If you look at earlier threads in the Spain section of the forum, you'll find some good ideas, often accompanied by public-transportation tips. In brief, and ignoring Andalucía since I haven't been there recently:

Barcelona
Girona (my clear #1, not having been to Montserrat)
Montserrat
For Dali fans: Figueres and Cadaques
Sitges
Besalu (best visited from a base in Girona, though)
Note that Barcelona has an unusual number of sights because of the modernista architecture. Don't prepay for much outside the city before knowing how much time you'll need for Barcelona itself. And read your guidebook carefully to determine which of the sights you want to visit require timed tickets, typically purchased in advance.

Madrid
Toledo (my clear #1, though the next two are also great)
Segovia
Cuenca (on the AVE line toward Valencia, so easily accessible by train, but the old town is too far to walk from the station)
Avila (to me far less interesting than the first three, all of which are worthy of overnight stays)
Alcala de Henares (I preferred this to Avila just for walking around, but it doesn't get many US tourists)

I think you might want to peel a couple of nights off Seville so you can see the Alhambra. I don't think that's a viable day-trip from Seville. If you do want to see the Alhambra, be aware that you must book your tickets way in advance.

Steve,

Have you considered visiting Granada?

You may want to visit Córdoba when in Sevilla, or as an overnight en route to Madrid.

Ah! To be you with three weeks to spend in May in Spain strikes envy among many people.
Suggest you consider flying into barcelona and out of Seville, this is termed an "open jaw" ticket and helps avoid backtracking. Even with three weeks, time is your most valued commodity on this journey.
Strongly encourage you to rent apts in each destination. More space, a kitchen, sometimes a clothes washer and often adds another level of immersion into travel experiences than hotels.
You do not need a car as train, metro and bus travel is ample and comfortable.
What hobbies do you enjoy at home? The point is with the time you have I encourage you to strive to find experiences matching some of your hobbies while in Spain. Example: we love tennis and have been able to attend several tournaments and also enjoy playing at some clubs while on our travels.
Barcelona is a rich diverse menu offering ample exploration within and outside the prime tourist areas.
Madrid is the third largest city in Europe and has a relatively small centralized main tourist zone. However there are several day trip opportunities well worth consideration. Personally I would spend less time in Madrid and more either in Barcelona or Seville.
Seville is another rich menu of opportunities and we enjoy day tripping from this locale.
Be sure and check for local festivals occuring at each destination and take advantage of these opportunities.
Most of all we find the people of Spain to be one of the highlights of our travels so we recommend walking out of the tourist zones and finding tapas bars to many with locals and challenge our tatse buds. Be adventurous with your tummys and accept the challenge of trying new foods.
Finally, toss aside your body clock and do stay up late. So much happens late in the evening by either eating on "cultural time", strolling through neighborhoods or attending concerts, etc. make the most of your time while in Spain.
Enjoy!

Thanks for these replies. Really helpful and provide more insight. I hope I get some more with this kind of feedback.

Great suggestions. Here are a few of my biased preferences.

Barcelona has so much to offer both in the city and for day trips by train that I'd allocate at least a week there. You can see the Dali "experience" in Figueres and Girona in one day.

Madrid is my least favorite city in Spain. There are lots of places to enjoy, but with a few exceptions they pale in comparison to everywhere else there. The major sights are the first class art museums. If you enjoy that, you'll want to devote at least 2 days to them. There's also one of the best palaces in Europe and a very interesting, enjoyable Naval Museum (bring passports to visit). Toledo can be a day trip from Madrid and that's the way most people visit, but it's much better as an overnight stay (or even 2-3 nights). I haven't been to the other "Madrid day trip" towns.

Seville is worth 2-3 full days and you can easily day-trip to Cordoba (or stop for the day en route between Sevilla and Madrid) and Jerez, but other towns are really too far for easy day trips. The Andalucian towns are too spread out from each other to make day-tripping a good option.

So consider moving around a little more. A week in Barcelona and 3-4 days in Madrid leaves you roughly a week and a half to move around Andalucia. If you stay in Jerez, you can day trip by train to Cadiz and by bus to Arcos. Granada is well worth 3 nights - there's a reason the Alhambra tickets sell out every day of the year. I'd fly into Madrid, then tootle around Andalucia and fly from Granada to Barcelona (there are cheap flights) and home from there.

Spring is festival time in Spain. Sevilla's Feria is hugely popular, as is the horse fair in Jerez and Cordoba has a charming (so I'm told) patio festival. Note the dates and take that into account in your planning. Read this article which explains the train system. You can get tickets at huge discounts if you buy early.

From Madrid leave time to day trip to Toledo and/or Segovia. An overnight would be nice but I get not wanting to move hotels a lot.

Ditto for Córdoba from Seville

And I 100 agree to spend 2-3 nights in Granada.

Ideally I'd do 6 Barcelona, 5 Madrid (day trips), 3 Granada, 3 - 5 more around Andalucia (beach at Nerja, or hill towns), and 4-6 in Seville.

You have some great suggestions already, so I will keep my advice short.

I think 5-7 days in Barcelona is too much. You can see Barcelona and Monserrat in 3-4 days.

5-7 days each is good for Madrid area as well as Seville area.

To each his own, of course. I spent ten days in Barcelona this year. That did not include Girona, Besalu, Cadaques or Montserrat. Now, I am a big fan of modernista architecture, and ten days would have been too much time (given all the other interesting places in Spain) if I had cut out all the funky architecture. However, Barcelona has a lot of interesting museums as well, plus the historic neigborhoods.

Thanks for the valuable feedback. These replies really help us create a plan that will allows us to see this beautiful country. Greatly appreciated.

This is an easy one with the luxury of 3 weeks.

5 nights each for Barcelona / Madrid / Sevilla.
3 nights in Granada for the Alhambra.
3 nights to visit the white hill towns (Ronda, Arcos) while travelling between Granada and Seville

Day trip options:
Girona and Tarragona from Barcelona.
Toledo and Segovia from Madrid.
Córdoba and Jerez from Sevilla.