If you guys are up for a good leg workout that doesn't require any equipment try the 30 down squats, I did them several times last summer.
You do 30 sets starting with 30 reps, then 29, 28, all the way to 1 with a minute break between sets, it gets too easy when you're down to the last 10 sets though, that's why I did 5 sets of 12 eventually seeing as there was no challenge towards the end.