A junior hydra chest is an item in Evony TKR (The King's Return). It can be found after killing certain monsters or bosses, with some of them listed below.
The description of Junior Hydra Chest in Evony TKR says:
Open the package to gain all the items in it.
Junior Hydra Chest is known to drop from a number of bosses or monsters upon killing, including Junior Hydra.
Note: This list may be incomplete.
Junior Hydra Chest opens up to all of the following items: