If you stay at Idle Awhile it’s Couple Swept Away sports center which is fantastic. There is also Exotic Fitness near Treehouse and it offers a workout with a view and across the street from Negril Beach Club there is a full gym. Last I was there it was $10 a day with weekly and monthly rates available. Remind your grandson to get an early start. None of these are air conditioned and it’s so easy to overheat or worse. Hopefully someone has information on the Westend gym. I heard it is a nice one.