Sometimes it’s nice to escape the city for a day of relaxation, but the weather isn’t cooperative or you simply can’t get yourself organized enough to traverse the Paris périphérique. So what can you do right here in the city to feel like you’ve escaped the noise and crowds? Try a day poolside in one of the Parisian palace hotels.
Unlike the public pools, they are not cheap. But for about €200 you can spend the day lounging in luxury surroundings in pristine, heated swimming pools with spa facilities including steam baths and saunas. Combine it with a relaxing massage or facial and a light gourmet lunch and you’ve spoiled yourself rotten for the day without the bother of trains, planes or automobiles. Here are a few that offer day passes:

Le Royal Monceau Raffles Hotel has a 23-meter indoor infinity pool and Clarins spa with detox treatments. All pristine white, designed by Philippe Starck, natural lighting from skylights. Day pass to pool, sauna, steam room and fitness €190 (free if you get any spa treatments of at least two hours). This is a very trendy hotel, so pack your most stylish bikini.

Shangri-La Hotel Paris has a Greek-style 15-meter mosaic-tiled pool which opens to a huge outdoor sundeck for plenty of natural light, designed by Pierre-Yves Rochon. Spa treatments by Carita. A day pass of €250 includes a 60-minute facial or body treatment and access to the pool, steam room and fitness. This hotel is known for its service, and has life guard on duty.

Hôtel Molitor just reopened in 2014 with two stunning Art Deco pools built in 1929, one indoors (33 meters under a glass roof) and one outdoors (46 meters, heated), along with a Clarins spa, steam baths, sauna and relaxation room. Day passes are €190, and at the moment it includes a 60-minute Clarins treatment (which was still offered when I called, even though the website said it expired in April). Lunch on the rooftop restaurant with views of the Eiffel Tower. Be sure to ask for a booking on a day when school kids are not using the pool! Note: the indoor pool is closed during Roland Garros.

If you don’t mind a short train from Gare St-Lazare, the Waldorf Astoria’s Trianon Palace Versailles has a large heated swimming pool beneath a glass atrium and overlooking the manicured hotel grounds. Spa treatments by Guerlain. A €150 Gold Club Beauté membership will allow you access to the pool, sauna, steam room, and outdoor deck, and includes a glass of Champagne and 60-minute spa treatment.
** Note: The pool at the Four Seasons Paris George V is one of the best in town, but only reserved for hotel guests (even if you schedule a spa treatment). **
Thank you Heather for the exhaustive review, and for the inspiration as we are building the first app to book hotel pools, in Paris, we already have the Fouquet's Barriere, the Renaissance Vendome, Les Bains de Léa..more to come.See you by the pool & have a great day(pass)
Paris' public swimming pools are indeed cheap, but hardly what I'd call "blissful", as they are usually crowded with screaming kids, often scruffy and in need of a good paint job, and you have to wear swimming caps and speedo-type bathing suits if you're a guy. And of course there are no towels provided, no poolside bar service, no dining area for a healthy lunch…Municipal pools are a great public service, but they're not the place to go to escape from the noisy, crowded city for a day of luxurious pampering. Although some journalists don't seem to know the difference when comparing the two: http://www.nytimes.com/interactive/2015/05/20/travel/frugal-traveler-in-paris.html
or get to know the bliss of the 38 Paris public swimming pools for a few euros – some absolute heaven some offer midnight swimming such as the Edouard Pailleron piscine in the 19TH ( reached by bus 48 or metro Jean Jaurès or Bolivar) and where you can skate too yes there is a patinoire open all year round check pool hours etc on www.nageurs.com ( if you know French) otherwise the English site of the city of Paris www.paris.fr/english and search out swimming pools, Enjoy!