13F Exterior is a location in Luigi's Mansion 3. It is found on the thirteenth floor of The Last Resort, the Fitness Center. It is accessible from the Yoga Room.
To access this area, Luigi must align the mats in the Yoga Room with the states of the respective posters on the back wall, opening a rotating wall to the northwest. From there, Luigi can access the 13F Exterior; though the floor initially appears intact, it slowly gives way as Luigi heads west, which features a treasure chest containing the key needed to access the Shower Room from the Yoga Room.