425-427 William Street offers a rare opportunity to acquire a distinctive, fully functional multi-level commercial property in the heart of London with exceptional flexibility for future use. The building features unique architectural character highlighted by a rare central carriageway "tunnel" connecting both sides of the property and providing access to a centrally located accessible entrance with elevator. Spanning three levels, the property is configured with over 17 offices, 4 clinic rooms with sinks, multiple common areas, and 4 bathrooms, supporting a wide range of professional, medical, or institutional uses. The main floor includes a reception area, treatment rooms, accessible elevator vestibule, three entrances, and an accessible washroom. The second floor offers 8 offices, a full kitchen, separate men's and women's washrooms, and common space, while the third floor features 5 additional offices, a common area, and a 3-piece bathroom. A fully operational elevator (inspected 2026) and dual staircases provide efficient access throughout. Additional highlights include a flex space for an office, studio, or storage located in the rear yard, 4-6 parking spaces at the front with potential for more at the rear, and updated mechanicals including furnaces (~6 years) and recent fire system inspections (2026). Zoned BDC/OR (Business District Commercial / Office Residential), the property allows for a wide range of uses including offices, clinics, retail, restaurants, residential units, and mixed-use development, with strong potential for residential or live/work conversion into multiple units. Not heritage designated and located just outside the East Woodfield Heritage Conservation District, this is a rare opportunity to secure a high-functioning, well maintained century building with strong conversion and redevelopment potential in a central London location.