The Pool at Hilton Denver City Center
The pool at Denver Marriott City Center is mentioned by experts. Of the 4 reviews tracked on TripExpert, 2 praised the pool, like Fodor's and Star Service.
Hilton Denver City Center 
Fodor's
Star Service
Fodor's "The indoor pool is nice, and the fitness center contains enough equipment to provide a well-rounded workout"
Star Service "One room full of aerobics machines overlooks the indoor four-lane lap pool, which is flanked on one side by a circular whirlpool and on the other by a formidable array of Nautilus weight equipment"
