Me and my friend did a tour of Spain and San Sebastian was the place that I liked the most beside Madrid. We stayed there for two days and a half. The weather was bad (rain and between 13-17°C) except for the last day but the city was beautiful even in the rain. The food is fantastic and you can smell the ocean from the moment you step of the train. The whole city is very clean and people are extremely friendly.
Insider Tip:We wanted to go on the Igeldo hill the first day but decided to wait till the next day since it was raining which was a big mistake. The next day the rain was even heavier and the whole hill was in fog. So if you want to visit it dont wait for better weather.