Inspired by Frank Lloyd Wright and classic mid-century design, this custom-built Castro Valley residence—offered by its original owner—is ideally located in the San Francisco Bay Area, approximately 30 miles east of San Francisco and about 35 miles from Silicon Valley. Set within the sought-after Proctor School District and bordering EBMUD Watershed land within the East Bay Regional Park network, the property offers great privacy, natural beauty, and abundant wildlife. Architectural highlights include vaulted wood ceilings with exposed beams, rich parquet flooring, multiple stained glass windows, and a dramatic fireplace constructed from Northern California boulders. The home features 4 bedrooms, 2.5 bathrooms, a dedicated office, private sauna with shower, and generous storage throughout. Outdoor amenities include a large swimming pool, mature landscaping, hillside views, and a horse stable. New homeowner may apply for Redwood Rangers membership, providing access to adjacent 600-acre cooperative pasture, trail system, and seasonal riding facilities. A rare opportunity to restore and elevate a distinctive mid-century modern home of architectural significance into a remarkable mid-century modern estate of enduring value. Some images have been digitally altered to show the property potential.