All is so quiet and serene in this new sunlit indoor swimming pool that it’s almost a shame to discuss the nitty-gritty of its construction. Retrofitted in an existing townhouse on Manhattan’s Upper East Side, the room occupies a substantial part of the building’s basement and extends under an outdoor courtyard. Pleasantville, N.Y.-based builder and remodeler John Ginsbern used steel sheeting, braced across the width of the building, to keep the neighbor’s yard from collapsing as he excavated 17 feet below grade. Limited equipment access meant that all the digging had to be done by hand. A room-width skylight illuminates the finished space, supplemented by a scattering of LED wall fixtures that can be programmed to change colors in rhythm with any musical selection. More project photos