The apartment is lovely and in a great place.
The view is breathtaking and constantly changing with different things going on (take binoculars).
Nearby cafe and bars are very nice and popular.
There are loads of shops nearby just off the main promenade for those who like that kind of the thing.
The walk along the promenade in to the ‘old town’ feels short with lots to see.
Parking outside is time bound so you can’t stay there very long during the day but you can leave it all night for free. Big car parks nearby are quite expensive. The nearest park and ride (which is free) is only 30-40 walk (mostly through parks and along the river promenade) for those who enjoy that kind of thing. A very good option if you’re not going anywhere for a few days.
Donostia or San Sebastián, whichever you prefer is a fabulous city with loads of very nice bars, restaurants and shops plus a while raft of other things to get up to.
On the beach surfing seems an option every day as well as any other thing you fancy getting up to on a beach.
Definitely worth a visit and this and apartment is is definitely worth considering - spacious, clean, well equipped, and in a great location.