A discreet treasure in one of Cape Cod's most prestigious enclaves, this exceptional 1.78-acre waterfront estate offers a beautifully preserved five-bedroom residence and a substantial deep-water dock with direct access to Nantucket Sound. Originally part of a historic compound long held by the Mellon family and now by philanthropist William Koch, the property presents a rare chance to own a slice of coastal legacy. Inside, the home features a main-level primary suite with study, stone fireplace, open-concept kitchen, and screened porch opening to an expansive deck with water views - perfect for entertaining or quiet reflection. Guest bedrooms upstairs enjoy generous proportions and stunning vistas. With additional buildable parcels also available, this is a unique opportunity to create a private compound in exclusive Osterville - renowned for its protected waters, world-class golf, and enduring Cape Cod charm.