The website is finally (with some delay) in English!
Here are a couple of facts on the 100k taking place in the South Pole. William participated in the 100k this year (21/01/2016).
Here is a picture of the route of the marathon. The 100k took place at the same time as the marathon (around 42k). The difference with the North Pole Marathon (check the website right here) is the wind. In fact, the South Pole is windier than the North Pole making it harder according to William. The temperature was around -20 degrees which is what William expected. No surprises concerning the temperature.