With stone and marble walls, bronze-detailed doors, and scrolled wood massage tables, the new spa at Ashford Castle in western Ireland’s County Mayo is the buzziest new spot on the global spa circuit—certainly the most opulent. It was the final component of the castle-hotel’s two-year, US$75 million restoration, which finished in November and now sees the former home to countless nobles and the Guinness family fitted with a hammam, manicure and pedicure salon, relaxation area, well-equipped gym, five treatment rooms, and a terrace overlooking the castle’s peaceful lake, Lough Corrib. The only thing to compete with such views is by the indoor pool, where South African ceramicist Jane du Rand created a dazzling mosaic wall mural inspired by Celtic folklore. —Gabrielle Lipton