Like some days earlier in St. Jean de Luz, also this appartment turned out to be taken by mould and impossible for us to stay in. Like in the previous similar bad experience, also here windows were open at the time of the check in. So we did not react to the smell at that point. The truth became apparent when we returned from the city in the evening. Luckily, this time we returned early enough to be able to move into a hotel still before the night and we did not have to stay a single night in this apartment.
Unfortunately, and like few days earlier, also this landlady did not make any gesture to compensate us anything and we lost the money of all the nights.
The area where the apartment is located, is nice, calm and has good quality gastronomic boutiques. The landlady also gave us some good advice about nice restaurants and cafes in Biarritz.
However, I have to conclude that if you do not wish to take a risk of living in an apartment seemingly suffering a problem of a mould, don't stay here.