In some locations you may find a "Secret Switch", they will usually open up an area for you to explore that is not required to complete the dungeon. In the area you may find other Hidden Treasures or rewards.
Much like Hidden Treasures, once discovered via the Light of Deldrimor, the Secret Switch resembles a small blue flame on the floor. Using the Light again while standing on or near the flame will reveal the switch, which must then be clicked on to activate.