Eschewing the strained decorative calisthenics endemic to contemporary summer residences in the Hamptons, we designed the interiors of this landmark manse as the simplest, most archetypal version of a beach getaway. Originally designed in the 1920s by Roger Bullard, the architect of the nearby Maidstone Club and other prominent historical sites. Yet despite the home’s patrician history and regal proportions, the owner was wholly disinterested in any sort of Gilded Age finery or contemporary swank. Instead, we covered the walls in subtly luminous white stucco and outfitted the rooms with unpretentious, tailored furnishings upholstered in simple white cotton—a dramatic counterpoint to the existing oak beams and monumental brick fireplace. Strategically placed vintage textiles and traditional patterned fabrics accent the design scheme without disrupting the prevailing atmosphere of understatement and ease. The one exception to our determinedly restrained approach is the capacious circular sofa that traces the form of a curious circular room, with a conical, wood-beamed ceiling, added in the 1970s. Covered in an archival Brunschwig & Fils floral chintz, the exuberant sofa somehow feels appropriate for this peculiar architectural folly.