In recent years the luxury spa has become as essential as restaurants and swimming pools in a hotel industry looking to expand profit margins and lure more guests. Once a mere gym and perhaps a few treatments rooms, the spa has emerged as a prime profit center for hotels and resorts looking to offer guests maximum amenities and fewer reasons to ever have to leave the property.

This trend hasn't helped everyone in the spa business. Golden Door recently was forced to shutter its iconic Greenhouse Spa near Dallas, created by Neiman Marcus' Stanley Marcus in 1965, as more and more potential guests opted out of multiday spa getaways in lieu of an afternoon visit during an overnight stay somewhere else.

The Beverly Hills Hotel's spa experience offers La Prairie's Skin Caviar line and VIP access to the hotel's swimming pool, even for nonhotel guests.

According to the International Spa Association, hotel-owned spas have tripled since 2007, expanding beyond five-star chains such as the Four Seasons and Peninsula to even three- and four-star chains such as

Hyatt

(H) - Get Report

, with its Pure Spa, and

Marriott's

(MAR) - Get Report

Elizabeth Arden Red Door Spa.

To distinguish themselves from their four-star competition, high-end hoteliers such as Paris' Plaza Athenee and St. Tropez's Byblos have sought relationships with big-name conglomerates and cosmetic companies including Dior and Sisley.

In Southern California the iconic

Beverly Hills Hotel

offers its La Prairie Spa amid tough competition with hotel-based spas including the Montage BH and nearby Peninsula Beverly Hills. Guests can book treatments such as firming facials that use La Prairie's Skin Caviar line and includes VIP access to the hotel's swimming pool, even for nonhotel guests, afterward.

L.A.-based hotels also face increased competition from the emergence of med spas that aim to pair Botox treatments and laser photo-light facials with the traditional massages and body treatments of a typical day spa such as Burke Williams and its new

Spa 7 Cosmetic and Laser Center

.

At New York's

Plaza Hotel

, Caudalie's Vinotherapie Spa was one of the first to bring the experience of a French wine chateau to the hotel's spa are. The spa incorporates classic skin and body treatments with such wine-themed amenities as a signature barrel bath and French Paradox Wine Lounge.

Other properties in the creme de la creme Caudalíe's Vinothérapie chain include Gehry-designed Marques de Riscal in Spain, Hotel Les Ottomans in Istanbul and Aux Sources de Caudalie at Chateau Smith Haut LaFitte near France's Bordeaux.

In Miami, a city with its own Canyon Ranch Hotel and Residences, San Francisco-based Kimpton Hotels opened one of its largest-ever properties last year with a freestanding luxury spa at

Epic Hotel

near downtown. This isn't just any spa. As part of L.A.-based Exhale Yoga and Spa, it offers a 12,000-sqaure-foot sanctuary of Vinyasa classes, a hair salon and 14 treatment rooms geared toward active yogis and holistic-minded travelers.

Lacking sponsorships and corporate brandings, other hotel spas have tried to upgrade their wow factor with signature amenities and one-off designs that include expanded services and specialized suites.

Also in Miami,

Soho Beach House

is the newest outpost of the exclusive London member's club that operates a series of open-to-the-public hotel spas in New York, London and Berlin. The company also operates an array of day spas under the Cowshed branding found in London and New York but that originated at its Babington House country property near U.K.'s Somerset.

Cowshed Miami Beach, open to all, is spread along two floors offering a stylish and eclectic design of distressed wood paneling and decor that blends old and new. The spa incorporates a traditional man's barbershop of checkerboard floors, Blow Dry bar for on-the-fly blowouts and full gym with regular beach-based fitness classes sure to be a workout fixture on the Miami celeb scene.

At the upcoming

Cosmopolitan Las Vegas

, set to open in mid-December, the state-of-the-art Sahra Spa & Hammam takes aim at such spa hotel heavyweights as THEhotel's Bathhouse at Mandalay Bay and Venetian-based Canyon Ranch.

Sahra Spa will include integrated light therapy throughout 18 treatment rooms and Turkish-themed vitality pools, as well as three luxury spa and penthouse spa suites that bring the spa to your room with steam sauna, side-by-side dual hydrotherapy tubs and multiguest treatment areas for you and your Vegas posse.

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Michael Martin is the managing editor of JetSetReport.com, a luxury travel and lifestyle guide based in Los Angeles and London. His work has appeared in InStyle, Blackbook, Elle, U.K.'s Red magazine and on ITV and the BBC.