But to any high-end hotel that hopes to stay competitive, the spa is a necessity.

The spa experience is becoming so engrained into American culture that travelers expect a state-of-the-art spa to be part of the hotel experience, like room service or valet parking, industry experts say.

"Hotel spas are now seemingly ubiquitous," said Mark Woodworth, president of Atlanta-based PKF Hospitality Research, a consulting firm. "Over the past decade, hotels across the nation have added spa operations to meet escalating consumer expectations and to increase revenues and profit."

Even the almost-100-year-old U.S. Grant Hotel in downtown San Diego is getting into the act with the planned construction this spring of a $5 million, 9,000-square-foot spa and fitness room.

Mark Dibella, director of media and community relations for the U.S. Grant, said the hotel is going for the coveted fifth star with the addition of the spa.

"The U.S. Grant always maintained a reputation in the mid-tier of hotels, but stepping into the luxury tier it becomes part of the international marketplace, and you have to have a spa component," Dibella said. "The indulgent services - the all-about-you amenities - are expected."

And for the financial bottom line, those services are desirable, hotel industry experts say. Spas not only help drive consumer decisions in lodging, but they are increasingly becoming an important profit generator for hotels and resorts.

A study of resort and urban hotel spas' expense and profit data for 2005 and 2006 found that a 9.7 percent increase in spa revenues resulted in an 11.3 percent gain in spa department profits in 2006, according to a PKF report released in January.

The 9.7 percent increase compared favorably with the 8.2 percent increase in hotel revenues and a 5.9 percent average gain in sales from all other hotel departments, according to the report.

"A spa used to be a support tool for a hotel; now it is really a business driver," said Rob Sapp, director of marketing for Four Seasons Resort Aviara in Carlsbad, Calif. "A destination resort will feature golf and tennis, but we are finding that the spa is also a key reason people come back. They want to rejuvenate and escape the pressures of work."

Aviara spent about $3.5 million to almost double the size of its spa in 2001. The 15,000-square-foot spa, which includes 20 treatment rooms, a solarium lounge, whirlpools, saunas and steam rooms, now generates the highest profit margin of any Four Seasons resort-based spa in North America and South America, Sapp said.

With the explosive growth of spas - there are an estimated 14,600 spas in the United States, with day spas making up the largest segment - many hotels are seeking ways to stand out from the crowd, offering increasingly exotic services or finding market niches.

As part of the recent $65 million makeover of San Diego's Hyatt Regency Islandia, renamed the Hyatt Regency Mission Bay Spa & Marina, the hotel is catering to the environmentally conscious crowd with Blue Marble, its "eco-friendly" spa.

In this case, eco-friendly means that the treatments and products used are organic, and so are the business practices. The spa embraces conservation, using energy-efficient light bulbs, low-flow showerheads and recycled paper products, and has floors of sustainable bamboo.

Kyra Johnson, spa director for Blue Marble, said Hyatt made a societal and corporate decision to go green.

"There is definitely a growing market for people seeking out greener options and ways they can reduce their own negative environmental impact," said Johnson. "And it is important for hotels to offer these lifestyle choices to guests."

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