This workout is super simple and you can do it anywhere. It is a good one to do when traveling, would run 1-2 km to a park or grassy area and then punch out this pyramid workout and run back again.
A pyramid workout involves working your way up, then going back down again - once you finish the 50 sit ups, you get to choose whether to repeat the 50 sit ups again. I usually don't!
Disclaimer - I am not a personal trainer, nor do I have any formal training in fitness or exercise. This is just a workout that I made up and thought others might like to enjoy. Please be careful and don't hurt yourself.