I think the stairs are one of the most killer forms of cardio there is. Next to full on sprints and hills, which are absolutely killer…the stairs seem to get me every time. Today I got on with the determination to do 40 minutes of intervals. It was a battle. 
I will be honest. Those first few minutes were rough, but I made it through! My workout went as follows:
- 5 minute warm up Level 10
- 2 minutes @ 12, 2 minutes @ 15, 1 minute recovery @ 8 (repeated 6 times)
- 5 minute cool down level 10
- wipe away sweat.
I was so happy I stuck it out once I was done. It felt great! I finished with a chest and triceps workout, and then called it a sweaty day. If you have access to some stairs, give this workout a try. You can decrease the intensity with lower levels, and increase the intensity with higher levels.