This is a nice run along the Oria River (Orioko Itsasadarra) river in Orio, which is located 17 km west of San Sebastián. There’s an option to add a climb on the paths to Orioko Hondartzako Behatokia, for some great views.

From the area of the train station, run on the road on the west side of the river toward Oribarzahar Hondartza beach. There are lovely views of the Oria river along this road for 1.75 km to the end (no sidewalk/shoulder, but a quiet road). After this 3.5 km out and back, use the N-634 road, which has a decent sidewalk, to cross over to the east side of the river, where there’s a pedestrian path along the river and marina for 1.6 km to Antilla Beach. Overall, just running the river paths is ~10 km.

Google Street View

Add-On: Orio Beach Observatory.  From Antilla Beach, there’s a good option to add on all or part of the Beach Observatory hiking path (Orioko Hondartzako Behatokia). It’s a wide path with good footing, featuring great views of the Bay of Biscay. Run up to 1.5 km to the end of the path at the Itxaspe Nekazalturismoa hotel. Note: 150m+ climb. There’s additional trail running in the Behatokia hills.