D4 is a luxe residential condominium conversion of an early 20th-century police station in Boston's South Boston neighborhood of 2006. Units range from 1- to 3-bedrooms featuring high ceilings, open floor plans, large windows, in-unit laundry, contemporary kitchens/baths, and designer finishes. The association comprises 25 residences on four floors with amenities such as concierge services, shared roof garden, elevator, and garage parking. D4 is pet-friendly with restrictions.