Since I'm tired of being the only one that knows where it is, I'm just gonna share since I've never had a team actually want to get it. The right, and ONLY the right portal must be open when atheon dies. Upon his death the fire team will walk into said portal and will not be greeted with a timer or distorted vision, instead you will see the past with clear vision now the giant triangle in the back of the room will be covered in vegetation and rock formations that look like platforms. Venture to the top point of the triangle and you prize awaits. Your welcome destiny community.