Milestone Adventure

The Chords of Chaos is meant to be a relatively low-level campaign. Characters of level 5 and beyond are meant to feel special, and characters beyond level 10 are meant to feel truly rare. Low Level Characters might not have the statistical power or the magical prowess of high level players, but this doesn't mean Low Level Characters cannot make a massive impact on the world. It is entirely possible for a King to be a level 1 character.
There are four level tiers in the campaign: Levels 1-4, 5-10, 11-16, and 17-20. When you reach the cap of your tier, you cannot gain anymore XP, nor can you level your character any further, until you go through a "Milestone Adventure" with Gambet, or an assigned Milestone DM.
Milestone Adventures are effectively a one-shot adventure designed to kill your entire group. Permadeath is on the line, and resurrection from Milestone Adventures will be nearly impossible. They are not to be undertaken lightly. If you are willing to put everything on the line to reach the next tier of play, you are welcome to do so.
If you successfully complete a Milestone Adventure, you will level up immediately, and will also likely be rewarded with fame and/or fortune to some degree.
While Milestone Challenges are designed to be extremely challenging, they will also be designed to be fun, interesting, and appropriate to the campaign and story. They are also designed with the specific group in mind, so powergamed characters are likely to experience a more difficult challenge than balanced, RP-focused characters. So don't feel like you have to powergame your characters because of this mechanic. There will be puzzles that might not require any rolls at all. Preparation is also important.
Milestone Challenges do not happen all the time, or immediately upon request. Gambet will do Milestone Adventures periodically, and is unlikely to do one for a group if they already did one recently, as we're not looking to see any groups blast through 20 levels in only a couple of months.