Are you starting to train for something?
Yes - I will run Big Easy next weekend. How much should I do before tapering?
You should do a training run of similar distance to be sure you can cover the distance.
Tick - it's only a 10-20k run. 10k flatish. 10k uphill which is just a nice walk. And 20k downhill. Downhill doesnt count. Cos Gravity. Ask the engineers.