The Proving Grounds is a new area of Yaesha added in Remnant 2's Forgotten Kingdom DLC that seems to be some ritual or trial that adults of the Pan are meant to overcome. It's an area full of deadly poison darts, vicious enemies, cruel traps, and more. But, on every level of this multi-floor puzzle gauntlet, there are rewards waiting for you to find, you just have to know where to look.