This was my attempt at making a gym that would fit the setting of DnD. This was used in my campaign that takes place in the city of Stormreach on the planet of Eberron. If you need inspiration, they were originally led here to reclaim some stolen goods (steroids) for the local weapons shop owner, which they could find if choosing the right locker in the locker room which I just mentally place in a random locker. If they happened to enter from the front, they found a character matching the description of a 'Wanted Poster' they had on their persons. He would be sparring in the center of the boxing ring, with several other people watching as it was a training facility. Feel free to use this how you see fit though for your own campaign and be as creative as you would like!