It's not particularly clear on Google maps but this gym is located with the Stones Hotel - enter from the beach front. You will then need to go to the health spa where someone will take 150,000 IDR off you and escort you to the gym.
At the time of writing 150,000 IDR is about £9 which is very over priced. The gym is probably the cleanest, newest feeling gym I've ever been in but the dumbells only go up to 20kg and there is no squat rack or bench - not even a smith machine. There is however a huge range of resistance machines and cables so it is possible to get a half decent workout in. Full range of cardio equipment also. More details & map below.
Details as of 01/09/2016:
Cost: 150,000 IDR per day
Dumbells: Up to 20kg
Barbell w/ plates: Approx. 140kg
Bench Press: No
Squat Rack: No
Entry Requirements: Trainers - No Flip Flops -_-