Just join the center memebership. Or walk in a pay for a class or to use the facilities. You can also look it up on Denver parks and recreation online.
Or stop by, printed schedules are available at the check-in desk.
If you Google Denver Rec Centers it will take you to the home page for all the recs, and from there you can find individual centers. When you go the individual center pages near the top there is a schedule of classes. You could always pop into the rec you are interested in and they have hard copies available as well.
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