Sure, I'll start by mentioning the incredible Seat61 website: https://www.seat61.com/Portugal.htm
Since you seem torn between the Basque country and Sevilla/Barcelona, why not do one each way. :)
I guess I'd start with Northern Spain since the return is faster with more high-speed trains.
Timetables for August won't be published for a loooong time but you can check the current times and there shouldn't be much change. Actually I'm also planning a Portugal trip in July.
Bordeaux, Hendaye or probably even San Sebastian should be reachable in a day from your hometown (unless you live in the North perhaps). The Euskotren from Hendaye isn't included in Interrail but only costs 3-4€ per person.
Alternatively get to Paris during the day, have dinner there and board a night train to Tarbes or Hendaye. I'm not sure it runs daily. You'll have to share the couchette compartment.
(No night trains in Spain and Portugal sadly.)
There's a metric gauge railway along the coast between Bilbao and Santander, even further to Ferrol. It is extremely slow but I've heard views are nice. Still debating whether I include it or not on my trip.
Fastest is usually via Madrid and to spend the night in Vigo. Following day Vigo - Porto - Faro/destination.
For the return something like:
- Day 1: bus Portugal - Sevilla
- Day 2: Sevilla - Barcelona direct AVE (6h)
- Day 3: Barcelona - Paris direct TGV (6h30-7h)
- Day 4: Paris - home
I mean Sevilla will be really hot guaranteed so stay calm during the day and visit after sunset. ;)
Thanks so much for your reply! Really helpful :-)
We’re north of Leeds so will probably stay in Paris, or go for a night train. But thanks - lots of useful tips.