A thousand square metres of stone and water beneath rue de Castiglione. Liaigre has closed a ten-year Costes redesign with an oxygen-enriched pool, eight treatment rooms, and a kind of quiet the hotel has never offered before.
The twenty-metre pool, Hôtel Costes, 7 rue de Castiglione
The Costes has sold a specific kind of Paris evening since 1995. Dim light. Stéphane Pompougnac compilations. People who want to be seen by other people who want to be seen. None of that has changed above ground. What has changed is the floor below. At half past eleven in the morning, you leave the noise of the upstairs bar and descend a bifurcated marble staircase into a room the hotel has never had before.
Jean-Louis Costes opened the spa on 15 April. It is the final move in a ten-year redesign that has folded three neighbouring properties, Hôtel Costes, Hôtel Lotti, and Le Costes, into a single address on the corner of rue de Castiglione and rue Saint-Honoré. The Tuileries are two minutes away. Place Vendôme is three.
The pool
Twenty metres of heated water, lit from below, sit in the centre of the room. The water is oxygenated. By mid-morning a thin layer of steam hangs at waist height and the pool reads as a still interior lake. Liaigre calls it a lagoon. The description is accurate.
There is no lane divider. Most of the people in the water are not swimming laps. They are drifting, face up, looking at the low travertine vault overhead.
The reception, designed by Studio Liaigre
The design
Christophe Caillaud led the project for Studio Liaigre. The materials are travertine, smoked oak, lacquer, and liquidambar, a North American hardwood that has been quietly returning to French interiors over the past two years. The palette stays low. Light falls from hidden coves. There are no overhead fixtures.
A Dolby Atmos system runs through the ceilings. The tuning is gentle enough that you notice it only when it goes silent, which happens during treatments. The bifurcated staircase lands at a reception desk cut from a single slab of marble. Beyond it, the room opens to the pool without any intermediate door.
The Costes has always been a room where people went to be watched. The spa is the first room here designed for forgetting the room above it.
Léa FontaineAugustinus Bader
The treatment menu is built around Augustinus Bader, the German biologist whose Trigger Factor Complex has been a fixture of industry bathrooms for five years. This is his largest branded spa anywhere. The eight treatment rooms run along a single hushed corridor, each behind a smoked-oak door with a brass handle set flush to the grain.
Sessions start at ninety minutes. The menu does not offer anything shorter. The therapists were trained in London at the Augustinus Bader flagship before the Paris opening. The TFC8 Rituel de Soin is the signature: cleansing, lymphatic massage, two serums, and a sleep mask applied under low light with a warmed compress.
One of eight treatment rooms
Ten years
Jean-Louis Costes began the redesign in 2015. The bar came first, then the restaurant, then the guest rooms, then the lobby. The spa was always the last piece. Its arrival makes the address feel finished in a way it did not before. Guests staying in the Lotti wing can now walk from their rooms to the pool without crossing a public corridor.
The verdict
By five in the evening the bar upstairs begins to fill. By seven the noise is considerable. The spa closes at eight, which feels deliberate. The two halves of the hotel are meant to stay separate.
Book a treatment for late morning. Swim afterwards. Stay below ground until the light outside changes. The Costes has finally built a room that lets you forget the Costes.
The Costes Spa opened on 15 April 2026. Day passes for in-house guests are complimentary; non-resident access is available by treatment booking only. The TFC8 Rituel de Soin starts at €450. Reservations through hotelcostes.com.
Photography courtesy of Hôtel Costes and Studio Liaigre, via Wallpaper*