There is a gym inside the college and it is for free. However, it is only available during some times. If you don't want to go there then you can go to PureGym which is located at the opposite road. The advantage of the PureGym is that it has various equipments for different needs unlike the college which has few equipments.
You could also go to southside and maybe watch a movie after the college. In the second floor, there is a Cineworld where you can watch different types of movies.