Paris is hosting the Olympics this summer so I wouldn't recommend to stay there at all. Expect crazy prices, crowds and security measures. Totally unpleasant and the city isn't that far from London anyway... :)
I'd travel one way via the Atlantic side and the other via the Mediterranean. There are night trains between Paris and the Spanish border.
Schedules for August haven't been published yet. France should do so on 13th March and Spain in the near future too.
One example between many :
- DAY 1 : London - Paris - Bordeaux
If you wish to avoid the station transfer in Paris, there are a few TGV intersecteurs avoiding the city. First take a Eurostar to Lille.
- DAY 2 : Bordeaux - Hendaye - San Sebastian
San Sebastian - Malaga would be best split in Madrid but expect the city to be very hot so idk
For the return :
- DAY 1 : Malaga - Barcelona direct AVE (more frequent if you change in Madrid)
In any case you'll have to book trains requiring reservations well in advance. It will be peak peak season.
- DAY 2 : Barcelona - Nîmes or Avignon (say in that area). You can take the slower coastal route if you wish to save on reservations.
- DAY 3 : either long day home via Paris or Lille, or you could spend a night near Dijon for example
Questions welcome. General link : https://www.seat61.com/interrail-and-eurail-reservations.htm
Hello! Thank you for this, great tip about avoiding Paris! I’ll have a look at those options :-)