10 nights Barcelona and Madrid

Since you say you’re very flexible, could you add some more days/nights to this trip?

I haven't been to Basque country but I wouldn't want to use up precious time going there and back (at least a 4 hour train ride each way). I'd split the time evenly between the two cities and incorporate a day trip or two from each. Plenty to do in each place. You'll use up a chunk of a day going between the two cities.

Separate trip in my opinion. You can check the train and plane connections to see if the there are options that suit you, but for me with only 10 nights and so much to see in Madrid and Barcelona, there would be too much travel time involved. The travel days are days often leave little sightseeing time in a location.

My first Madrid (only) trip was 8 or 9 nights. We had no trouble filling that time in Madrid with day trips to Segovia and Toledo. Brought home a list of sites and day trips that we didn't have time to see.

I'm about to leave on a 7 night Barcelona trip. I had no problem filling the itinerary with "must-sees".

Edit - Cross-posted with CL. We seem in agreement!

Spain is a big country and very diverse. I understand the temptation to see it all, but revisits will prove to be much more satisfying. Splitting ten days between Barcelona and Madrid will fill your interests. Save the Basque region for another time.

For me there's definitely not time to cover Barcelona, Madrid and the Basque Country on a 10-night (9-day) trip. However, August is really a better time to be in the Basque Country than in Madrid (especially) or Barcelona. Most of Spain tends to be very hot in the summer; the Basque Country is more likely to be cool and overcast.

Take a look at the actual, historical, day-by-day weather statistics for Madrid on the website timeanddate.com: Madrid weather -- August 2023. You definitely should check additional years (use the pull-down box at the right, just above the graph), because weather varies a lot from year to year. However, August 2023 indicates how bad it can be: 24 days with highs at 90F or above, 17 days at 95F or above, 11 days at 99F or above and 6 days at 100F or above.

RS Best of Spain Tour begins in Barcelona for 2 nights ( though most travelers will have an extra pre-tour night before the start) and then 2 nights in Madrid before proceeding south. The RS Basque Country of Spain & France in 9 Days Tour does 2 night in San Sebastián and 2 nights in Bilbao.

As you can see the RS tours separate them into two tours (as many here recommend) but the choice is yours. Spain is wonderful so whatever you decide you'll have a great time!

Good luck!

Independent travelers should not anticipate moving from place to place as rapidly as professionally escorted tours.

RS tours do indeed make getting place to place easy and predictable, good point! I recall reading Rick's advice if you have X days, what would you see? And then he'd add days and places. His pace was always action packed. But that's not for everyone. Pace is a personal choice and you can actually move faster as an independent traveller than with a group-- no waiting for the group, no stopping every 2 hours for bathroom breaks, you can fly, you can use the train, you can rent a car and so on. Ah be young again! At my age I tend to agree more and more with the advice to slow down -- but my wife still wants to always pack in the extra site! and go the extra mile! The good news is either way you still get to see Spain!

Happy traveling!

10 days between the two is fine. Try for 4 days in Barcelona with a day trip to see Andorra or Black Madonna if you are spiritual. 3 days is a good overview of Barcelona. You’ll get to do one of each “type” of thing - 1 walking tour, one Gaudi house, one FC Barcelona thing, Sagrada Familia. You won’t get into the details of the city, but you’ll see enough over 3 days.

Don’t see enough time for 3 different locales frankly.