At the Locksmith shrine...
- For using 1 key to unlock a chest it's 1000 gems per attempt (500 gems for Hero of Htrea)
- If you fail you will lose the key and gems only
You need Weak key, Skull key or Master key to open Near empty treasure chest, Half full treasure chests or Loaded treasure chests.
Weak keys have lowest chances of opening any of the chests, Skull keys have a little higher chance and Master keys have the highest chance.
You can purchase a Master key for 5 Painite.