What it’s like inside a spa run by the Agua Caliente band of Cahuilla Indians

Forget Marilyn Monroe and Frank Sinatra for a minute. Forget mid-century modern design and consignment stores selling Cher’s old pool statues. Even forget the Coachella music festival, because unless you know about the sacred portal to the underworld, you haven’t begun to understand Palm Springs.

Few people leaving the frozen yoghurt store on the corner of Indian Canyon Drive and Tahquitz Canyon Way realise they are near the mouth of the sacred Séc-he spring. This spring (meaning “the…