Secret rooms are hidden rooms that can occasionally be found inside dungeons by scouting ahead.
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.
To enter a secret room, it has to be scouted first and it must be critical scouting only. 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.
With the release of The Crimson Court, secret rooms can also 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.
Scouting has a chance of occurring whenever a new room is entered or certain curios are activated, making nearby unexplored areas less risky to traverse. A high scouting chance can also cause parts of the map to be already scouted at the start of an expedition.
Scouting chance is effected by torch level, trinkets, and quirks. Certain curios can also give scouts (sometimes these even scout the entire dungeon!) radiant and dim light increase your scouting chance, but lower light levels do not decrease or increase it.
When scouting is triggered, nearby rooms and corridors on the dungeon map will be revealed, showing their contents. Depending on the successfulness of the scouting, one or two (in case of critical scouting success) nearby corridors may be scouted. Scouting will always depart from the current position towards unexplored directions. Scouting is also the only way of revealing secret rooms, which can be revealed only during critical scouting success.
By scouting ahead, it is possible to reveal incoming dangers in advance, giving the player a chance to reroute to avoid unnecessary risks or save on torches by skipping empty rooms and corridors. Scouted traps are an easy source of stress heal for heroes with good disarm chance and scouted battles will prevent the party from being surprised.