4 rounds, each for time, of:
Bike 1 mile
Rest as needed between efforts.
Use a stationary bike or find a 1-mile course to repeat each round.

Notes: Simple workouts are the hardest ones. They depend solely on your effort, and that's added difficulty. This one right here is one in which all that matters is that your perceived effort is 10/10. The rest between rounds is free, which means every set is all out.

2:30
2:36
2:32
2:26