A decent-sized apartment in a fantastic location - five minutes walk from the main beach and Les Halles (the glorious covered food market, with buzzy bars/restaurants along its sides). It's also two mins from the bus stop (get the no.11 to Jardin Public from the airport - it's pennies, and takes about ten mins).
Like others have said on the comments, the apartment definitely isn't worthy of four stars! It's perfectly serviceable, but very basic. Many of the floor tiles are crazed (with slightly grubby grouting), and our shower was leaky. Also don't be fooled by the housekeeping staff in the halls - we stayed six nights, but they didn't ever come in and clean or change our towels. The other thing is it's VERY noisy at night. There's no aircon, so if you have your windows open - we were facing the street - you get no end of people wandering past, talking loudly, and motorbikes/delivery vans/binmen etc, even though it's a side street. Others have suggested getting an apartment overlooking the gardens instead - we were late bookers, or would have done the same.
But it's... fine. No real issues. And Biarritz is brrrrrrilliant! Good choice!