The Fitness Center at Narai Hotel
The fitness center at Narai Hotel is endorsed by those who travel for a living. Of the 5 publications tracked on TripExpert, 2 praised the fitness center, like Oyster and Fodor's.
Narai Hotel 
Oyster
Fodor's
Oyster " There are smoking and nonsmoking floors, a good-size fitness center, and an outdoor pool large enough for moderate lap swimming"
Fodor's "A slightly claustrophobic gym has a bright red concrete floor with some basic cardio and weight machines"
