A 19th-century illustration of the women's bath inside of Leukerbad, a spa in Switzerland. —clu—Getty ImagesSummer, for many of us, has its own comforting set of rituals. People pull out the barbecue, open fire hydrants, throw block parties. Maybe there are road trips, visits to grandparents, pool days, beach days. Maybe there’s a lake or an island and a ramshackle old house where the breeze comes through the windows at dusk every evening, the s…