The Chamber of the gems is located within the castle of Lireo, guarded by multiple Lirean Soldiers. Inside the chabber are multiple artifacts, including (formerly) the four elemental gems.
2005 - 2006
The gem chamber is where Mine-a used to keep her crown when she is not wearing it, as well as the four elemental gems. In the 2005 Series, it is a room guarded by several soldiers. The space where the gems are kept are being surrounded by a wall that levitates whenever someone(presumably a Sang're or Queen) commands it to.
2016 - 2017
The chamber is where Mine-a keeps the gems whenever she goes to sleep. It is also where the important treasures and items of Lireo are being kept.