A lavatory monument assembly configured to be positioned in the interior of an aircraft. The modular lavatory monument assembly includes first, second, third and fourth walls that cooperate to form an enclosure that defines a lavatory interior, a door positioned on one of the first, second, third, or fourth walls, and an opening on the fourth side that is open to an exterior of the enclosure. A seat is at least partially positioned in the opening. The seat includes a seat back and a seat portion that is pivotal between a storage position and a deployed position. In the deployed position the seat portion extends outside of the opening.