Northern Spain to Portugal

Just returned from the areas you are considering. We flew to Porto, spent 3 days there, then trained to Lisbon (about 3 hours) and spent a week. Visited Sintra (nice but extremely crowded on a Monday). Flew then to Bilbao and biked for 5 days into San Sebastian. The coastline between the two is amazing. Renting a car in Portugal or Spain and returning it in the other country proved to be expensive, so we went the train/ plane route.
From what the locals said, your time frame (late July, early August) will be very crowded with tourists. Not that that should make you change your plans - just be forewarned.
Food in San Sebastian was amazing. Didn't get to Arzak, but did go to a 2-star and a 1-star restaurant for lunches. Tasting menus were around 85-100 euros and well worth the price. Pintxos in the many bars/ restaurants were a great deal.
Suggest you read Rick's books on both countries as there is a lot to see and do.
Enjoy

Hi, I would personally choose a car as the means of transportation for this trip. The north of Spain is not as well connected yet by train as the east/south are (especially if you want to go from Spain to Portugal). A car would be your best bet. As there may be an increased charge to drop off a rental in another country and because there are already quite a few sites between Barcelona and Santiago de Compostela, I would also consider possibly dropping the Portugal portion of this trip and leaving it for another time.

For potential stops you could do:
-Start Barcelona - spend at least a few days then start heading west.

-Poblet Monastery - a UNESCO World Heritage Site, a still active 12th-century Cistercian monastery located in western Catalonia - one of the largest in Spain. It was a fortified medieval royal residence and now contains the unique hanging tombs of the Kings of Aragon.

-Zaragoza - Capital of the Aragon region. More than 2,000 years of history including Roman ruins of the city walls and amphitheater and the Aljafería, an 11th-century Moorish palace. It also has the famous pilgrimage site of Nuestra Señora del Pilar basilica, housing the miraculous image of the Virgin Mary.

-Royal Palace of Olite - For me, one of the most impressive medieval castles in Europe. The seat of the Kings of Navarre. There is a also pretty good Parador hotel next door.

-Pamplona - If you go in early July you may be able to catch the Running of the Bulls Festival (San Fermin). If not it is still worth a short stop.

-San Sebastián
-Bilbao

-Santillana del Mar - Well preserved medieval town in the Cantabrian region. Known for its medieval towers, Renaissance villas and the Romanesque Santa Juliana Collegiate Church.

-Altamira caves - UNESCO world heritage site located near Santillana del Mar with numerous Paleolithic cave paintings. The real caves are closed to the public but there is a pretty good replica cave and museum there too.

-Picos de Europa - Mountain range between Cantabria and Asturias offers some of Europe's most spectacular mountain scenery. Make sure to stop at Potes, an atmospheric medieval mountain town.

-Covadonga - known as the "cradle of Spain", a pilgrimage site dedicated to the Battle of Covadonga of 718 AD which set off the Reconquista. There is also a Holy Cave, where lies Kings Pelagius and Alfonso I, the first kings of Asturias.

-Oviedo - The capital of Asturias. Known for its Gothic medieval old town, apparently Woody Allen's favorite city in Spain.

From there you can drive on to Santiago de Compostela, although I would not know of smaller stops along the way as surprisingly I have yet to visited Galicia. As you can see three weeks may only be just enough to see Northern Spain alone.

I agree with renting a car and also that 3 weeks is barely enough time to see northern Spain. I spent 3 weeks there last year and could have used additional time. Other possible stops in addition to those already mentioned, Zumaia, Getaria, Muxia, Leon, Burgos, Ponferrada, Alto de Cebreiro, Cathedral Beach near Ribadeo, Cartuja de Miraflores just outside Burgos, Monte de Gozo just outside of Santiago de Compostela. What you see will be determined by the route you take, northern along the coast, or inland.

I agree with the others that northern Spain and Portugal are two separate trips if you have only three weeks. Most of the places I visited have already been mentioned, but here are a few additional possibilities in Galicia: A Coruna, Betanzos, Pontevedra, Combarra, Cambados. The last two are quite small and touristy. And I liked Vitoria-Gasteiz and Hondarribia in the Basque Country.

Mid-summer is an excellent time to visit most of the places mentioned, because it tends to be cool and wet. A Coruna for some reason is drier/warmer. Zaragoza can be miserably hot during that season (average high 90F, record about 110F), and both Pamplona and Leon are far enough from the coast that they don't have the same moderate temps as the other spots. You won't have time to go everywhere, so you may as well take expected weather into consideration. Personally, I think Pamplona is imminently skippable unless you specifically want to see the bulls run, in which case you should be looking for lodging now.

I think that Carlos has laid out a good itinerary but I would make one change. From Zaragoza I would head north to Huesca and Jaca. Both are nice to visit, and there is the Castle of Loarre, just outside of Huesca, which was used in the Ridley Scot movie Kingdom of Heaven. And just outside of Jaca is the Royal Monastery of San Juan de la Peña, where the Holy Grail was keep for a few hundred years. The parador of Sos del Rey Catolico is also very nice. (Sorry Carlos, the parador in Erriberri (Olite) is very Disneylandesque for me)

If you do go to Pamplona, late July is a good time to visit. The San Fermines end the 14th, and the city has a "resaca" or hangover. Things are very calm, and best of all, all the blue parking zones are free for the rest of the month.

dlindstrom makes a good point regarding an alternative route, from Zaragoza one can also head north towards the foothills of the Pyrenees, where there are also many historical sites. I am also a fan of Loarre - a very picturesque castle, definitely looks like something out of a 19th century romantic painting.

Once you reach Jaca you can turn west and continue towards Pamplona/San Sebastián.

However if you do take this route then you will probably bypass Olite which, in addition to its fine castle, also has a well preserved partially-walled medieval town. I'd say that it's on par with the likes of Ávila and Carcassonne.

Carlos instead of saying "a well preserved partially-walled medieval town" it might be better a "well rebuilt". The palace was heavily damaged in 1813 and only in 1937 did a rehabiliation project start that lasted over thirty years.

Many of the castles and forts of Navarra have been destroyed or badly damaged over time. The castle of San Francisco Javier, for example, is also a modern rebuild.

One thing Olite had going for it as of 2016 was that it was pretty much undiscovered by foreign tourists. In that sense it reminded me of Extremadura.

dlindstrom - I guess they did a pretty good job with renovating/restoring because I did not even realise that the palace had been heavily damaged, thanks for that insight :)

Yes unfortunately between the Napoleonic invasion, the Carlist wars, and the Civil war, many historical sites in Spain have been damaged. However there have been some really great restoration efforts all around I think. For example the Medieval Bridge in Besalú (northern Catalonia) was completely destroyed during the civil war in the 1930s, but one would not even think that nowadays, as it has been completely and authentically rebuilt.

Many newspapers have multiple articles on Spanish travel, like the Guardian.
Bilbao city guide
Galicia coast holiday guide
Slow train through Spain
etc.

Carlos the funny thing is that it was the Navarros who burnt the castle so the French couldn't use it.