The Fitness Center is the thirteenth floor of The Last Resort in Luigi's Mansion 3. It is accessible after obtaining this floor's elevator button from Captain Fishook at The Spectral Catch. When Luigi reaches the Gym Lobby, he tries to get into the Locker Room. After he realizes that the door is locked, a ball hits the window. Luigi looks through the window and sees Johnny Deepend flexing in a swimming pool. Johnny throws another ball at the window, and Luigi gets attacked by a Slinker and some Goobs wearing hats and sunglasses. The last ghost to be captured drops the key to the Locker Room, where he encounters an Oozer that hides in the lockers. Mini Goobs and Mini Hammers are also hidden in the lockers and will come out when Luigi slams them.
In the Weight Room, there is a Hammer wearing boxing gloves and another one lifting weights. The boxing gloves and weights protect the Hammers from the Strobulb, so he must trick the weightlifting Hammer into tossing his weight into the Hammer with the gloves to stun him and capture him, then use the gloves to stun the Hammer with the weights. After beating them, Luigi can enter the Training Room and get a key by spinning one of the exercise bikes with the Poltergust G-00. It unlocks the Yoga Room, where Luigi has to roll up the mats to match how they are laid out in the mirror. Once the mats are laid out correctly, the wall opens up, allowing Luigi to reach the 13F Exterior and obtain another key. When Luigi tries to continue, ghosts appear and trap him in the room until they are defeated. In the Shower Room, the steam from the showers protects the ghosts from the Strobulb, so he has to turn them off before he can attack them.
At the pool, Johnny Deepend starts throwing balls at Luigi. To disarm him, the pool must be drained. Gooigi can get through a fence on the right to reach a valve that drains the pool, but Johnny will try to melt him by squirting water at him, so Luigi needs to stun Johnny by hitting him with a ball so Gooigi can get to the valve and turn it all the way. After draining the pool, Johnny gets stuck in the drain. Luigi can now hit him with another ball and vacuum his goggles to make him vulnerable to the Strobulb and capture him. He drops the elevator button that leads to the fourteenth floor, The Dance Hall. However, when Luigi takes the button back to the elevator, Polterkitty steals it, necessitating that Luigi track her down.