During the war between the First Spinjitzu Master and the Overlord, the Overlord created a temple that could protect him from the First Spinjitzu Master's golden power.
Now the temple is located in New Ninjago City. It serves as a fortress of solitude; a place of peace. Most elemental powers are blocked and cannot function within the temple.
In many ways, it is a dark counterpart to the Temple of Light.