Used to be that when the snows melted and bikini season beckoned, well-to-do women would steal away to a spa and sup on the diet du jour. (Think grapefruit slices and a wheatgrass shake.) But as the body-tune-up industry has discovered the profitability of a male clientele, some spas have turned into adventure camps. The Red Mountain Resort & Spa in St. George, Utah, offers tough hikes along the red-earth cliffs, attracting celebs such as Chris Noth and Courtney Thorne Smith. They still cool off with a detox shake, however.