Sun Valley Legacy Estate & Development Masterpiece. Discover the pinnacle of mountain living at 120 Keystone St, a premier 52-acre legacy estate in the exclusive Elkhorn area of Sun Valley, Idaho. This rare dual-parcel landholding (18.6 & 33.5 acres) offers a breathtaking canvas for a private horse property or a high-end boutique residential development. Search address on YouTube for video tours.