One of One. Rarely does a property combine architectural significance, extraordinary scale, and a true beachfront setting so effortlessly. Set directly on the San Francisco Bay in Tiburon, La Casa Dei Quattro Orizzonti (the House of the Four Horizons) is a remarkable 6,721 sq. ft., 5-bedroom, 5-bath modern estate offering exceptional privacy and seamless single-level living on a 5.33 acre mostly level lot that flows directly to the white sand beach and the Bay. Designed by noted Italian architect Andrea Ponsi, featured in numerous architectural and design publications, and built ground-up by Red Horse Constructors, the residence draws inspiration from California mid-century modernism. Conceived as four pavilions arranged around a serene interior garden courtyard, the home is defined by extraordinary scale, abundant natural light, strong architectural sight-lines and expansive, retracting walls of glass that create a continuous connection between indoors and out. The thoughtful design provides exceptional separation between grand scale public living spaces, the private primary wing, guest accommodations, and functional spaces including a 3-car garage. An art collector's dream, the public areas incorporate extensive gallery space while maintaining an open, light-filled environment for everyday living and entertaining. Distinctive design details enhance the spaces, including copper accents, custom lighting, vaulted ceilings, and modern Italian cabinetry. A dramatic central axis draws the eye from the entry through the home to the water, while expansive terraces and decks step gently toward the shoreline, where water activities, a spa, and the beach beckon. The gardens abound - from an orchard garden at the entry and a private Japanese garden adjoining the primary wing to flower and herb gardens and the native landscape along the Bay. Conceived in harmony with its exceptional setting, the eco-friendly home incorporates passive solar strategies, natural ventilation, photovoltaic solar and environmentally conscious materials, including ipe wood-slat ventilated exterior walls, copper roofing, and solar glass canopies. Private yet remarkably accessible, this is a singular Tiburon beachfront estate: an exceptional convergence of significant architecture, sustainable design, single-level living and an intimate connection to the San Francisco Bay.