When John F. Kennedy convalesced at Castle Hot Springs following his World War II duty, he didn’t have Instagram to distract him. Founded in 1896, the health and wellness resort catered to prominent clans like the Kennedys, Roosevelts and Wrigleys before falling into disrepair and closing in the 1970s. Following a multimillion-dollar renovation, it reopened to the public last year, and launched its current season in October (it’ll be open through May then close for...