PPA redesigned the interiors of this apartment with full-bodied details, giving this narrow triplex penthouse, set within a 25-foot building designed by I. N. Phelps Stokes, an architectural sensuality. By reframing the steel on the upper part of the building and reengineering the space, PPA was able to open the rooms and create axes framed by broad elliptical arches. Katie Leede’s decoration enhances the architecture and art collection in this Fifth Avenue aerie.