When you get to the center of Cauldron Rho in Horizon Zero Dawn, you will see that there is a large machine in the center of the room that Aloy will say is a Blaze Processing chamber. The quest log will say
Find a way through the Blaze Processing Chamber
The quest marker will be pointing at the platform in the middle of the room, but there is no way up. Here is what you need to do to get up there.
How To Get To The Blaze Processing Chamber
I spent quite a lot of time on this, trying to hang on the boxes that were moving around the ceiling and what not. Turns out the solution was right in front of me. I guess those red triangle vents made it hard to see. If you go to the opposite side of the room from where you entered, you will see that there is a standard override switch that will get you over to the other side. Here is a video showing you how to get to the blaze processing chamber.
For a full guide on how to complete all of the cauldrons in Horizon Zero Dawn, check out the Cauldron Walkthrough guide.