Rusted Key

Description
This opens a lock somewhere. Unless the rust gets to it first.

Drop and usage
Found inside five chests in Warmaker's Sanctuary. They can be used in the final boss room to open four side doors that give access to extra chests that contain additional.

All five keys are in the prison area between the Inner Sanctum door and Arena door.
 * The first key is in the first cell on the left after descending the staircase. Use the launching trap inside the cell to reach the upper level. The chest is against the back wall.
 * The second key is up the stone stairs in the cell on the right at the intersection. After climbing the stairs, turn around and head into the back room where there are three beds lined up. The chest is next to the third bed.
 * The third key is on the left side after the intersection. Use the launching trap by the collapsed bars to reach the upper level. The chest is in the corner on the right.
 * The fourth key is up the stairs in the right-side cells down the intersection toward He-Who-Walks-Below. At the top of the stairs, turn around and head around them to find the chest on some shelves between two wooden crates.
 * The final key is up the stairs in the cell on the left at the end of the intersection by He-Who-Walks-Below. At the top of the stairs, continue straight forward around a buttress. On the other side, the chest is hidden in a pile of rubble.