The apartment is very clean and in a nice neighbourhood with everything we needed including good wifi reception. We slept well but just under the duvet sheets as it was too warm under the duvet. We walked everywhere including to the old town and the main beach. There is a supermarket around the corner. One day we hired bikes (hire place 10 min walk near the beach) as San Sebastián has plenty of cycle lanes.
Be careful when taking a shower that you don't get the bathroom floor full of water! Also a guest book for guests to write down tips and recommendations would be useful.