Situated on a quiet court in a desirable hillside neighborhood, 1509 Lassen Court offers an exceptional combination of space, flexibility, and value. With five bedrooms and multiple living areas, this home is well-suited for growing households, remote work, multi-generational living, or anyone seeking extra room to spread out. Recent improvements include a new roof and gutter system, newly paved driveway, refreshed landscaping, brand-new range, ample kitchen cabinetry, fireplace, and beautiful hardwood flooring throughout. A truly unique feature of the home is the hidden lower-level flex space beneath the house, constructed entirely of solid concrete and accessed by an interior stairway. Measuring approximately 10' x 20' with roughly 7.5-foot ceilings and ventilation, this rare bonus area offers endless possibilities including a wine cellar, media room, hobby or art studio, fitness area, safe room, workshop, or additional storage. Enjoy partial city views and a covered backyard patio perfect for relaxing or entertaining. Conveniently located near schools, shopping, dining, Mare Island, and easy freeway access. This is a rare opportunity to own a spacious home with a one-of-a-kind bonus space in an established Vallejo neighborhood. (Some photos have been virtually staged.)