re: Spain for 3 wks, no itinerary, no restrictions, any recommendations?

Any particular reason you need a car for the duration? Traveling around probably your best bet but might be easier and cheaper (and maybe less stressful) to just use trains and only rent car if needed (and even then can probably ride share).

I dont know if Real will still be playing in a month, but if the liga is still going, I was able to get tickets to a FC Barcelona match by going to the stadium on the morning of the match. Might be a similar system at other liga stadiums.

Barcelona, San Sebastien, and Pamplona are all great cities and all share a fierce sense of independence and difference from the rest of Spain. Barcelona might just be the best eating city in all of Europe. Have tons of restaurant recs if you want them.

Have fun and dont overplan is my best advice.