During the Old Friends quest in God of War Ragnarok, you will reach an area where there is a large piece of metal rubble blocking the path forward. This happens during the section of the quest where you need to Speak with Jormungandir.
There are two steps to clearing this. First, you need to walk along the path and up to where the rubble is. On the left side, you will notice a chunk of metal sticking up into the air. Shoot this with one of the stun arrows and it will cause the metal to crumple up.
In the next stage, you need to turn around and take the path to the side. This will bring you up above the rubble. If you look closely inside the metal tube you will see another glint of green that you can shoot with your arrow in order to clear a piece of metal that will allow you to crawl through it if you head back down
If you are unsure what you need to do here, check out the video guide below and it will show you how to progress past the rubble during the speak with Jörmungandr objective in the old friend’s quest.