There really isn't much in the downtown area. There are a couple of the new Gold's gyms 15 min. or so from downtown though to the East or West side of Cincinnati. If you look on Gold's website you'll want the one in Western Hills or the one in Beechmont to be the closest. New large facilities with full line of Hammer, tons of cardio equipment, etc but also plenty of jackoffs there to socialize.
If you want hardcore you'll be traveling about 30 miles north of Cincy.