A rare architectural offering, this one-of-a-kind 1956 Mid-Century Modern X-100 prototype, designed by an acclaimed team of architects, represents a pivotal moment in mid-century modern design. The home showcases six exposed steel I-beams, eliminating interior load-bearing walls and creating a dramatic open, light-filled environment with seamless indoor-outdoor flow. Thoughtfully restored while honoring its original vision, recent updates include fresh interior/exterior paint, recoated foam roof, refinished vinyl and concrete floors, updated radiant heating, curated furnishings, and refreshed landscaping. The home is organized around two private garden atriums with in-ground planting beds, while 32 feet of skylights flood the interiors with natural light. Signature materials, steel, glass, and Formica, highlight the home's authentic modernist character. Built-ins and kitchen elements are fully integrated into the architecture. Debuted in 1956, the X-100 gained national attention and influenced generations of modern residential design, set against the backdrop of Crystal Springs Reservoir. Listed on the National Register, this is a true collector-grade property ideal for design enthusiasts, historians, and those seeking a singular living experience.