Best gym in Cincinnati by far is the Mercy Healthplex. It is on the east side of town but they also have a couple other location (one is north, can't remember the other).
Xavier does have a nice masters swim program that meets (I believe) Mon - Wed - Fri in the evening. Some of the people in that group do rides before / after too.
Another nice place is Tri Health fitness pavillion -- near kenwood.
Downtown is tough but i hear the Y is decent. Nice running routes from downtown though, either up thru eden park or accross the purple people bridge. do you have a car? xavier university has masters swimming M-W-F.