This guide will tell you where to find the legendary chest in the Strond map in God of War Ragnarok. You will need to get past the rock part and then you can get to the chest on the other side. Throw your axe at that rock to hit the seal and break the door.
You have to kill the enemies on the other side, then go down and grab this thing as shown in the image below.
There might be some explodey slugs, so you need to be careful of those. Once inside, you will find the legendary chest.
