Inside a $35 Million Seacoast Estate | 518 New Castle

518 New Castle Avenue is a once-in-a-generation chance to own one of New England's most remarkable waterfront estates. Privately set on 7.7 acres on Portsmouth's coveted Shapleigh Island, this landmark Shingle Style residence offers complete seclusion on the Piscataqua River, just moments from downtown Portsmouth. Spanning 13,451 sqft across 17 rooms, the home offers 6 beds, 7 full & 2 half baths, and walls of windows capturing sweeping water views. Georgian-inspired millwork, Tuscan columns & intricate wainscoting define interiors of rare craftsmanship, from the soaring two-story foyer with its sweeping curved staircase to the great room with gallery balcony, a chandelier-lit dining room, and a wood-paneled library. Seven fireplaces, a chef's kitchen with copper-hooded range, butler's pantry, two wet bars, a sun room, game room, wine cellar, and a second-floor gym with sauna complete the living spaces. The primary suite opens to a private, column-lined veranda over the water, while a first-floor in-law suite with its own kitchen offers space for extended family. Outside, manicured lawns roll down to 185 feet of private beachfront, a deep-water dock with direct access to Portsmouth Harbor & the Atlantic, and a boat house. A heated gunite pool, columned pool house with stone fireplace & outdoor kitchen, bluestone terraces, and a shuffleboard court are made for grand entertaining. A lantern-lined private drive leads to a circular brick motor court, an attached 3-car garage, and a separate 2-car garage with a 1-bed, 1-bath guest apartment above. With a new roof completed in 2025 and nearly 6,000 sqft of unfinished lower-level space ready for future expansion, 518 New Castle Avenue is a rare opportunity to own one of the Seacoast's defining legacy properties. 📍 Portsmouth, NH | Represented by Mitch Varley, Realtor® , The Bakhtiari Group at Compass.