Century: Age of Ashes

Currently Century is in Season one. I reached level 100 in what seems like 3 weeks. First, complete all the daily, weekly, and season challenges. Doing just that got me to around level 80. Not sure if this was intended or not, but after all the season challenges were done and the week finished out the season week 12 challenges would reset and could re-do those 7 every time. Sometimes it seemed like it would reset after a few days, but it definitely did for me every week. This seems like the fastest way. It's a little bit of a grind and I was worried that once the next season comes levels would get reset back to one. Hope this helps!