The industry has never been the same.

"With the development of The Mirage as more of a resort facility starting to encompass a destination-type feel, that would have been the biggest landmark," said Jennifer Lynn, director of the new 50,000-square-foot Qua Bath & Spa at Caesars Palace.

Lynn, a 14-year industry veteran, got her start on the Strip as a personal fitness trainer for Wynn before opening and operating the spas at Treasure Island and Bellagio.

She said the current growth that Wynn seemed to foreshadow mirrors a higher number of people viewing spas as an alternative means for relaxation and health.

"If a hotel doesn't have a spa component it could be detrimental to their future," said Arzu Delp, spa director at Red Rock Resort. "It is what people look for nowadays. It's part of the relaxation, part of their vacation."

Spa revenue nationwide surpassed domestic box office receipts for theater movies in 2005, posting $9.7 billion compared to $9 billion, statistics gathered by the International Spa Association show.

"Las Vegas truly has become a spa mecca," Spa magazine Associate Publisher Ken Leandro said. "It has introduced some of the finest, most opulent spas. It's a booming area and a natural extension of what you see with the restaurant scene in Vegas."

Gaming companies do not release revenue numbers for individual amenities, so it is hard to gauge the Strip spa industry in hard numbers.

The 5-year-old Las Vegas Spa Association is gathering revenue and customer numbers from its members, which includes 60 spas and vendors, including Strip properties.

"Spas have become an essential focus for investing capital," said Lynn, who is also a board member of the Las Vegas Spa Association. "After 15 to 20 years of solid development, it is no longer really an amenity but now its a profit center for the property."

She said that nearly 45 percent of Qua's customers are also casino customers.

The spa industry has become so essential that gaming companies have integrated spas into their customer loyalty programs.

Although the luxury spa growth has been focused on the Strip, locals casino operator Station Casinos has also entered the market.

The gaming company first added a spa with the opening of Green Valley Ranch Resort in December 2001.

That spa was originally 10,000 square feet. But demand led to 20,000 square feet being added during a $15 million expansion of the property in 2005.

Red Rock Resort opened in April 2006 with a 30,000-square-foot spa and another is being designed for Durango Station, a hotel-casino Station plans to build near Durango Drive and the Las Vegas Beltway.

Delp said the Spa at Red Rock Resort sees a lot of customers from the casino floor but the company declined to give specific numbers.

"You get a lot of pent-up energy and a lot of pent-up frustration on the gaming floor," Delp said. "This is a good place to come to release that negative energy."

She said 20 percent of the spa's customers are male and that 40 percent are locals. At Green Valley Ranch Resort, nearly 60 percent of the spa customers are locals.

Like the rest of the industries tied to the building boom in Clark County, the spa industry could also be facing shortages of workers in the near future, said Michael Garvey, president of the Las Vegas Spa Association.

"Vegas is a very unique market," he said. "Nothing compares to what goes on in Vegas. It's like everything else in Vegas, it's off the charts. I think it is a very unique market because of the concentration of resort hotels and what they're trying to sell."

And what Las Vegas is trying to sell is the whole entertainment experience beyond just the casino.

The University of Nevada, Las Vegas introduced its first "Introduction to Spa Management" class last semester through the school's College of Hotel Administration.

Garvey said the plan is to grow the curriculum until a whole spa management course is developed.

"Everybody wants to put in a spa but they don't realize the spa won't be any good ... unless you get the best people in there," Garvey said.

Large spas are included in the $3 billion Cosmopolitan, $2.9 billion Fontainebleau and the $600 million Hard Rock Hotel redevelopment.