Since it was converted into a hotel, the former summer mansion of Napoléon III and Empress Eugénie has attracted royalty and celebrities in droves. However, one thing that didn't reflect the stellar status of the Hôtel du Palais was the fitness room - located depressingly close to the outdoor pool lavatories.
All that has changed, following the opening of its Spa Impérial last summer - though, perhaps demonstrating that builders are the same the world over, it didn't quite manage to open its doors to impatient hotel residents in July as promised in the glossy brochure.
The offering includes a female-only terracotta hammam, and a separate slate-grey one for men, his-and-hers cold plunge pools and saunas, a Guerlain spa with nine treatment rooms, a hair studio, a gym boasting sea-views and an indoor pool capped by a Jacuzzi.
The whole shebang cost a whopping €10m (£7m) to build, but it is the biggest spa on France's south-west coast. The spa, spread over four floors in a building once occupied by hotel staff, adjoins a further two levels which include a crèche and relaxation area. It offers an array of top-to-toe treatments from Indian head-massage to medical foot-therapy. If you have to opt for just one, choose the shiatsu massage in the Japanese-style room which will unwind knots you never knew existed.
When you feel suitably pampered and purified, you can re-toxify with a glass or two of champagne in the Salon d'Eugénie and watch the Atlantic rollers crash on to shore.
The Hôtel du Palais in Biarritz was decorated by Philippe Belloir, who revamped the Ritz hotels in Paris and London. It has the feel of a luxury ocean liner, and is decked out with signed photos of guests including Winston Churchill and Coco Chanel. If you can tear yourself away from the spa, the hotel's outdoor pool area offers celeb-spotting opportunities. I clocked Kylie playing cards with her (now ex-) boyfriend Olivier Martinez in the shade of their cabana.
Spindly blondes with partners whose weight mirrors their bulging wallets, and families accompanied by nannies, are also part of the scene. For nutrition, you can go from grazing on your sun-lounger to the gastronomic delights of La Villa Eugénie, and everything in between - including great room service and canapés to accompany your Bellini beneath the chandeliers of the Bar Impérial.
Hôtel du Palais, 1 Avenue de l'Impératrice, 64200 Biarritz, France (00 33 5 59 41 64 00; www.hotel-du-palais.com). Set on a hill, it overlooks the sea and dominates the beach below, which you can access through a manned gate. Designer shops are a short credit-card-busting walk away.
Time from international airport: 15 minutes by taxi from Biarritz airport.
At this level of luxury, you can expect to feel as peeved as the princess with the pea under her mattress if there is the merest hint of discomfort. Owned by Biarritz City, the hotel is conscious of its history. Its décor is traditional and opulent, although its spaciousness lends a light touch. You should be more than happy with any of the 154 rooms, but if you are fabulously flush and fussy, book the new fifth-floor penthouse.
Freebies: all rooms have toiletries stamped with the Napoléon Eugénie initials.
Keeping in touch: rooms have satellite TV and internet access.
THE BOTTOM LINE
Double rooms from €310 (£221) excluding breakfast.
I'm not paying that: join the surfers kipping on the beach in the summer, or if you want something less exposed to the elements, rooms at the Hotel Florida (00 33 5 59 24 01 76; www.hotel-florida-biarritz.com) start at €80 (£57) excluding breakfast.