Discover a rare opportunity in a prime Castro Valley location! This well-maintained duplex sits on a massive lot, offering endless possibilities for expansion--build additional units, add ADUs, or create your dream outdoor retreat (buyer to verify with county). One unit is currently vacant and move-in ready, featuring fresh interior paint and brand-new carpet, ideal for an owner-occupant or to attract quality tenants. The other unit provides steady rental income, making this a smart investment with immediate upside. Inside, both units offer bright and functional living spaces with charming vintage touches. The expansive backyard is a blank canvas--perfect for gardening, outdoor entertaining, or future development. A detached shed adds storage or workshop flexibility. Conveniently located near top-rated Castro Valley schools, BART, shopping, and commuter routes, this property combines potential, location, and versatility. Don't miss out on this unique investment or house-hacking opportunity in one of the East Bay's most desirable communities!