You will need something to stand on for a stretch (a block, the spotter's stand on an incline bench, etc). Either using body weight or with dumbbells do single leg calf-raises while standing (try 10 per leg) and then do raises with both legs to failure. Follow that with the same exercises, however, this time bend over so that your torso is parallel with the floor.
If the gym has a smith machine, you can get additional loading by using that instead of the dumbbells.
I'm sure others will have better suggestions, but these have worked well for me in the past.