They are structures in every act 2 of a mystic realm level, they can be pretty easy to distinguish from the rest of the level, they use the textures from arial garden zone, and have a platform in the middle, jump on it and a message "**** **** mystic temple has been activated" (**** the level) nad at the end of the stage you'll get wrped to another level, which usually has a theme based on the previous act, at the end of the level you'll find a chaos emerald.
JCZ1>JCZ2>JCZ3
JCZ1>JCZ2+mystic temple>MKZ1+emerald>JCZ3