I have one last golden chest to open at Saint Albanes Abby. The best have all been easy. This one is inside the main church building. There was a flag bearer inside. There is a room where I can see the chest but it is barricades with rubble and wood. It looks like it can be destroyed but my attacks do little to damage it.
I’d you go outside the main door into the courtyard and go to the right. You will find a tent that has some explosive jars. These are the red ones with a small flame on top. Pick one up and you can throw it at the room that is blocked off. When it detonates it will destroy it and allow you get at the last chest.