This was my wife's favorite Airbnb or our entire 3-week trip. We have one more stop to go, but I'd say it's mine as well.
The location is perfect in that you're in the heart of downtown San Sebastian, a few meters away from Playa Concha, which is a nice leisurely beach (not to be confused with Zurriola, which is the surfing beach, but also not that from it either), and you've got great sound insulation from the hullabaloo in the streets below, due to the double pane windows.
The apartment inside is also very comfy and warm feeling. We made much use of the washer and dryer -- which, after 2 weeks of traveling, was much welcomed. Leaving candies and fruits for is was a nice touch, along with other little goodies in the fridge. But don't get yourself too full on those, so you can make room for the pintxos -- which has got to be one of a few (perhaps, many) reasons why you're coming to San Sebastian.
As far as communication with our host, Narea, went, it was top notch. She checked in with us the day before, and kept in touch with us throughout our stay. To add to this, she wasn't able to check us in, because she was traveling herself, but she still took the time to find out if everything was okay. She had a friend named Tania who checked us in, and she was very helpful, sweet, and informative. (She even gave us a tip to stop in Laguardia before we reached our intended destination, Logrono.)
Lastly, the bed was comfy.
This place gets my highest seal of approval as thee place to stay in, if you're looking to be in the old town area of San Sebastian.