You will find several locked chests in the form of frogs. Here’s how to open them.
There is an Old Prisoner in Fallgrim Tower. This is a story character. He will ask you to bring him 3 glands from three different temples. As soon as you get to the first of the three main bosses, you will receive iron after his death. Leave the temple and see that Fallgrim is mired in fog. This fog removed all robbers and familiar enemies from the location, but populated it with some kind of bloodsuckers.
But it is precisely in the presence of such fog that Boiled Frogs become active. Interact with them to open chests.
Note that as soon as you give the Gland to the Old Prisoner, the fog will clear. However, another character will appear in the tower of Fallgrim. For 1 Glimpses, it will activate or deactivate the fog.