A nice steady endurance ride looking to not stress the body too much but still work the aerobic engine. The changes in cadence allow the body to get used to the different stresses placed upon it by the variation in cadence.
An endurance based session looking to work on the strengths and weaknesses you may have in your speed/cadence work.
Ride at a self selected cadence and throw in an 8sec burst every ten minutes. Keep the bursts seated and and then return to normal cadence for the next increment.
Do what you need to and loosen out a little
Vary your cadence during the Z3 portion and ensure adequate food and drink intake, best to eat during the Z2 portions of the effort.
Concentrate on a smooth pedalling style throughout and be aware of any niggles which may benefit from a positional analysis or bike fit.