The Fitness Center at Washington Marriott at Metro Center
Washington Marriott at Metro Center's fitness center is endorsed by professionals. Of the 6 reviews that we tracked, 2 recommended the fitness center, like Travel + Leisure and Oyster.
Washington Marriott at Metro Center 
Travel + Leisure
Oyster
Travel + Leisure "Other hotel amenities include an on-site restaurant, fitness center, indoor pool and spa tub, and a ground-floor Starbucks"
Oyster "A comfortable, reliable option just steps from a Metro subway hub and near the Verizon Center sports arena and the Washington Convention Center -- the 459-room Marriott doesn't get points for flash, but it has better service and a better gym and pool than the massive Grand Hyatt, around the corner"
