This is a fantastic apartment with a perfect location for visitors to San Sebastian. It's huge, with a very comfortable couch, and comfy beds. It's so big that, with the two full bathrooms on opposite ends, multiple friends can each feel like they have some privacy.
The balcony and terrace overlooking Constitucion Plaza are really great. Ignacio was a very responsive host and the place was spotlessly clean. The kitchen was large and well equipped (though in San Sebastian the food is so amazing we had zero interest in cooking)!
The only reason I'm giving it 4 stars instead of 5 is because of the noise at night on weekends. We stayed Wednesday - Saturday. On Wednesday and Thursday nights, noise was not an issue. But on Friday night, the noise of people partying in the street was very loud, and it was hard to sleep even with windows shut and earplugs in. This is not something within control of the host, obviously, and Spanish people love to party, so it's just something to be aware of.
Nevertheless, I recommend this apartment and we really enjoyed our stay!