It is actually a lovely walk, no highway or motorway. If you take the old bridge, which has no motor traffic, you will tracing back the steps of Spanish refugees during the Civil War, I felt something special as I walked that particular stretch and thought about all the Spaniards who fled Spain in 1936-1939... only to end up in the IIWW operation theater and then in concentration camps.
see this map, just follow the small road, hardly any traffic (red line I drew on top), and once you are in Irun, just follow the streets normally. Incidentally, where I mark the red circle, you will find Singular, a restaurant where teh day's menu, at 16 or 18 euro, is just from out of this world.
Hendaye was also the rendez vouz point where Hitler and Franco met one day to discuss possible alliances. Franco was 30 minutes late, Adolf was not impressed, and that probably determined the evolution of the II WW, at least for Spain.