Switzerland’s Grand Resort Bad Ragaz has mineral waters, saunas, and myriad treatments—all in one place.The Tamina Therme outdoor pool at Grand Resort Bad Ragaz.Credit: Grand Resort Bad RagazAs a wellness journalist and the author of the book "150 Spas You Need to Visit Before You Die" and the spa-focused newsletter Spascape, I’ve been to my share of impressive spas. Whether it’s an intimate urban retreat in Paris or New York City, a multiday Ay…