From the moment you arrive, the stature & grandeur of this remarkable residence are unmistakable. Welcome to the Upton Sinclair House, an iconic Spanish Colonial Revival estate originally built in 1923 & recognized as a Registered National Historic Landmark. Among the most storied homes in the City of Monrovia, this architectural treasure was purchased in 1942 by Pulitzer Prize-winning author Upton Sinclair, whose legacy remains deeply woven into the fabric of this extraordinary property. A custom stone-arched entry & handcrafted wood, wrought iron & glass front door introduce interiors rich in period detail & craftsmanship. Hardwood floors, intricate crown molding & a stone fireplace anchor the living room, which is framed by French doors that bring in abundant natural light. 2 of French doors open to a covered side patio, blending indoor & outdoor living. A masterfully carved wood archway with detailed pocket doors leads to the formal dining room. Multiple French doors open to intimate balconies & the side patio, creating an elegant setting. An intricately designed swinging door with stained glass detailing leads into the kitchen, where classic character meets thoughtful updates. Stone countertops, iconic black & white checkered flooring, stainless steel appliances & a cozy breakfast nook overlooking the garden. Pantry storage & access to the finished basement, currently housing laundry & a flexible bonus space, adds both charm & functionality. A custom interior wrought iron gate from the living area leads to the staircase to the 2nd level & a convenient 1/2 bathroom. Once upstairs, a barrel-ceiling hallway leads to 3 generously sized bedrooms. The primary suite features a decorative fireplace, multiple walk-in closets & French doors opening to private balconies. The ensuite bathroom accessible from both the hallway & primary showcases custom tilework, a pedestal sink & a glass-enclosed shower. Outdoors, a stone-laid patio with a covered lounge area & outdoor fireplace creates the perfect setting. The property includes a detached 2-car garage, bonus studio/storage space & a charming ADU with a kitchenette, 3/4 bathroom, a Murphy bed & a flexible living area. Thoughtfully designed landscaping & garden spaces wrap around the home. This rare offering combines architectural distinction & historical provenance, all supported by the financial benefits of a Mills Act designation. A once-in-a-generation opportunity for a true Southern California landmark