The Gymnasium was an area used for personal fitness and training by the crew aboard Red Dwarf.
The hologram Arnold Rimmer once swapped consciousness with Lister, promising to use the gymnasium to get Lister's body fit. However he didn't do this and instead used the hot tub of the Captain's quarters. ("Bodyswap", Series III)
- The extended hot tub scene eventually included in The Bodysnatcher Collection, reveals that the Caligula Suite did indeed have a gym as well as the hot tub; Rimmer just simply couldn't be bothered to use it.