Secret Room

Secret room is a hidden room that can occasionally be found inside dungeons by scouting ahead.

Content
Secret rooms will always contain a unique curio: the Ancient Artifact, which will drop a small quantity of valuables or, if opened with a Skeleton key, will provide several pieces of loot similar to that obtained when defeating The Collector, hence why the Artifact is regarded as containing "Great Treasures". As for every item providing loot, additional items are awarded if opening it while at low or zero light level.

Accessing secret rooms
To enter a secret room, it has to be scouted first. When scouting, eventual secret rooms will appear along a corridor; their position will be indicated by a golden star icon. Upon reaching the corridor segment holding the hidden door to the secret room, the room has to be accessed by clicking in the background or pressing the up arrow as would be done to enter a regular door. Once explored, the secret room can be left by clicking on a new destination room.

The Crimson Court DLC
Secret rooms in the Courtyard can hold prisoners. Prisoners are similar to experienced recruits; they start at higher levels and will have their weapons, armor and skills upgraded to the highest their current resolve level will allow. After you leave the quest, a rescued prisoner will be found in the stagecoach. Prisoner rooms appear only in the dungeons leading to the bosses: Baron, Viscount, and Countess.

Trivia

 * There is a secret room on the way to the final boss with the letter from the Red Hook.
 * Secret room counts towards the progress in the Explore quest.
 * Scouting via curio interactions will not reveal secret room.