OK, so this apartment is really nice. Bright, spacious with a fantastic peaceful view of San Sebastián. The beds are comfortable and the kitchen modern and extremely well-equipped.
The only drawback of this apartment is its location at the top of a steep hill. According to Google Maps it takes 19 minutes to get to the tourist office in Centro by foot (21 minutes return, because of the hill) but most visitors would want to go to the Old Town which is about 5 minutes further, or the main beach which is further again. The steps into town which are the most direct route are very very steep and very very many. Because of this, we would not recommend this apartment for people with mobility issues or people with babies, strollers or small children who don't easily walk very far. There are no shops or cafes at the top of the hill near the apartment so bear in mind that beach gear, provisions etc will all need to be carried up and down. Mikel did recommend a pedestrian elevator that has been installed but we found this of limited use since it brings you out quite far away with consequently a longer walk into the centre than taking the steps.
Also, the wifi is not wired internet. It's a mobile dongle which connects to the 3G mobile phone network and is very slow. Internet used to be in the apartment but there was a problem with it so If you rely on internet, check with Mikel to see if it's been re-installed.
Mikel, the host lives just down the hill which should be handy but he is obviously busy with other commitments and we had some queries and questions that still took a while to answer and resolve. Once you get him in person though, he is charming and friendly, and keen to be of assistance.
We weren't able to park our car in the garage as the height limit into the garage was 2m10 - our car is 2.5m high with roof box so it's worth knowing if you'll fit as it's impossible to find any kind of parking for non-residents in the centre of San Sebastián. Luckily there are a small number of unrestricted street parking spots out the front of the apartment.
Overall the apartment is a very lovely space to spend time in.