Its been many years since I was there, but I believe that hotel has an excellent gym. I used to sometimes make the drive down from Leeds when I was there on business and had to stay the weekend.
And for fans of snooker, you can make a side trip over to the Crucible Theatre, though it would be to take in a performance instead of snooker at that time of year. But there are (were) several pool halls in the city if you want to partake in a match or two.
There are several small towns within an hour of Sheffield that are worth visiting - and it used to be that there were public busses that went to places like Chesterfield, Castleton (caves) or Doncaster (which has a racetrack). IF you like hiking the Peak District national park is nice. If you like cricket make the hour or so drive up to Leeds to Headingley Cricket grounds. If they have one of those 20/20 or whatever it is now its an enjoyable evening.
There is a LOT to see within a few hours of Sheffield - especially for the younger guys that would like to get a bike and cycle around. For the old folks a rental car accesses much of the same scenery
Hope those that go enjoy themselves!