15 min Challenge
I saw this "challenge" several years ago on the internet but do not recall the source so I cannot give credit to the originator. Just making it clear that I did not create this one.
dumbbell backward lunge off of a low step (aprox 8 - 12 inches) and return to step and perform 2 arm curl. Repeat backward lunge/step up/curl on other leg. Doe total 6 reps. Each lunge is 1 rep so 3 per side. Then, without rest do 6 pushups with a mountain climber between each push up for 6 reps. Repeat as many of these circuits as you can in 15 minutes. I suggest fairly light DB's for the first exercise. For the pushup/mountain climber I used the elevated push up handles to increase the difficulty. You could shorten this to a 5 to 10 minute challenge to make it more like a finisher. I think in 15 minutes I was able to do 10 or 11 rounds and was pretty well spent. By the time you get to the 3rd or 4th round you will be feeling it.