SOLVED
Update: I think I found it, there is a nighbus to Castets
Hello I’m looking for suggestions to travel from San Sebastian to Vielle-Saint-Girons. No trains I guess but also I cannot find bus routes 
Tips and/or a good route planner for this area are welcome!
Thank you
you have the choice-and its most iikely not worth using a pass(day) for this.
There is a tram/train thing,run by EUSKotren (a hive off of old FEVE=the narrow gauge network along Biskaya coast), ev 30 mins fromDonostia (thats the name in Basque now) to French border: urin ESside, then Hendaya/e=FR side. Very cheap-can only buy tickets there. There also are a few buses-more aimed to serve the settlements in between end these end at Irun anyway.
LOCal trains in FR are always organised by the regions, named TER, this region is New-Aquitaine. Find more info on ter.sncf.coim-then find region. There will be a wealth of chepaper local fares.
IF you just use google there will be a host of since a few yrs all kind of sites that promise to offwr these solutions-like omio, moovit or others. Take a peak and see what they suggest-and do that with a kilo of salt, as its often much outdated. But it may sometimes give unexpected other means.
I also have no idea where this Fr village is-I assume not too far from border, but if its way up in FR-then use the general FR planner from Hendaye.
There's a regular bus service (Dax - Vielle-Saint-Girons) only in summer and then only in the weekends:
To get to Dax: Euskotren to Hendaye and then a TER to Dax.
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