Welcome to 303 Castlefield Ave, Waterloo-a rare opportunity to own a stunning newer custom-built executive home loaded with upgrades on a premium oversized lot in highly sought-after Colonial Acres. Offering 4,100+ SF of finished living space, this beautifully designed 4 bed, 4 bath home blends timeless style, exceptional craftsmanship, & modern family functionality on a stunning 68' x 171' lot surrounded by mature trees. Step inside to a welcoming front foyer & bright open-concept main flr designed for family living & entertaining. Stunning Barzotti kitchen with quartz counters, custom cabinetry, pantry, oversized 9' island, & seamless connection to breakfast area with deck access, great rm, & formal dining rm. Warm & inviting great rm with gas FP, stone surround, custom built-ins, shiplap detailing, & oversized windows overlooking the private backyard. Separate main flr office ideal for working from home. Functional mudrm with custom built-ins, backyard access, garage entry, & 2-pc bath. Upper level offers 4 generous bedrms incl spacious primary retreat with double closets incl lrg W/I closet & beautifully finished 4-pc ensuite with dual sinks & oversized shower. 3 additional sizable bedrms, 5-pc main bath, & upper-level laundry. Fully finished basement with over-sized rec rm, home gym/den, storage, & 3-pc bath with heated flrs. Walk-up from basement to garage creates excellent in-law potential. Hardwood & porcelain tile throughout main & upper levels. Designer lighting, pot lights, California shutters, & custom window coverings throughout. Expansive private fenced backyard with mature trees, spacious deck, patio, covered back porch, hot tub, & future pool potential. Impressive curb appeal with covered front porch, concrete driveway, & oversized garage with workshop area. Prime location-close to parks, trails, universities, shopping, Conestoga Mall, transit, major employers, & quick HWY access. Don't miss out on this incredibly rare opportunity in Colonial Acres!