... cos it's Donostia, not San Sebastián.
At least, that's what you'd think when you're looking for signposts for the city. It seems people still call the city by its Spanish name, but the Basque name dominates on signposts and train timetables.
And here's a tip for the next time you're in Irún (and you've done all the cigarette shops) and you decide to take the Euskotren to Donostia/San Sebastián: you won't find either name on the local map in the station; get off at Amara. Obviously!
I did the excursion yesterday and dipped my feet in the sea on the fabulous Playa de La Concha, right in the city. I'm going back today for a proper soak. It's slightly cloudy, so I might even take my shirt off...