While far from the center of town and certainly a big step down from Hilton's fabulous stay and sweat option, this Marriott provides a worthy athletic-minded alternative, especially for those with business in the immediate vicinity. Notably, this Marriott is the tallest hotel on the continent. Yes, you read that right, tallest on the continent. While this can mean beautiful views of the city, guests should anticipate potentially long elevator rides.
Quarters throughout the 44-story building have typical Marriott décor: conservatively solid color tones, basic furnishings (desk, tv, chair), and WiFi internet access ($fee applies). Marriott's comfy "Revive" bedding promotes healthy sleeping with soft sheets, fluffy duvets and relaxing pillows. Bring or buy snacks if you typically eat after midnight as room service is not 24/7.
The first floor gym is complimentary to hotel guests and open 24/7. It is staffed during the day. The ambiance inside is very uplifting - bright, modern and well-spaced. Machinery is top notch - Life Fitness's newest line of equipment - but a hotel of this size (588 rooms) should stock a few more bikes and ellipticals. I guess you have to hope that the mostly European clientele doesn't care about sweating on the road. Two rowing machines are rare athletic-minded treats as are the Smith machine and free weights. Audio and visual entertainment is attached to the cardio pieces.
Swimmers are out of luck as Marriott's only water option is a whirlpool. It'll be tough to accrue meaningful yardage out of it but potentially appealing as a post-workout relaxation treat. The only legitimate lap pool downtown Frankfurt is housed at the Fitness First adjacent to the Hilton, but it's only for guests of the hotel.
Joggers can head out to a crushed stone path encircling a pond across the street (maybe a quarter-mile in length) and can also follow it (the path) inside the road's median toward Palmengarten and Grunebergpark.