Secret Room
Secret Rooms are rooms hidden behind a wall.
Number of Rooms
There are usually two secret rooms per floor, however while playing Othermine sometimes floors generate 3 secret rooms by default.
Some items can increase the number of secret rooms that can be found on a floor.
Adventurer's Hat gives a 50% chance of floors to generate an extra secret room
Golden Idol does the same thing that Adventurer's Hat does
Circinus 25% chance of spawning an additional secret room attached to a secret room (this happens once per secret room and crawlspaces count as secret rooms too)
This means that it is possible to find anywhere between 2 and 8 Secret Rooms on a single floor in Undermine and between 2 and 10 Secret Rooms in Othermine these numbers are not including story related secret rooms as well. With story related secret rooms the maximum is likely 14 in the Contested Bog in Undermine.
Connectivity of Rooms
A room can have more than one secret room connected to it.
A secret room can be connected to more than one room, including another secret room.
One important use of this second point is that secret rooms can be used to get into Shops and sometimes other locked rooms without a 
Key by expending two 
Bombs one to get into the secret room and then another to open up the wall between the secret room and the shop.
Rooms in general (including secret rooms) can only be connected via the 4 main cardinal directions ie North, South, East, and West.
A secret room entrance needs some space to stand on against the wall that is being bombed.
Each room has custom coded information on which directions it can connect to in the game files.
Type of Rooms
Secret Rooms can contain puzzles, basic items, blessings, shrines, treasures, and dogs.
Special cases
Finding Secret Rooms
If there is a Secret Room attached to the room you are in when an explosion goes off three sparkles will appear in the center of the wall that can be bombed to access the secret room. This explosion can be generated by:
- the player's Bomb
- a
Troll Bombardier - a
Ogre Bombardier - a
Ogre Annihilator - a
Ogre Firestarter - a
Land Mine - a
Ticker - a
Poison Mine - an
Unstable Barrel - an
Unstable Crystal - a
Bomb Pilfer
Interestingly Enemies that have an explosive type attack can open secret rooms as well, even if they don't generate an explosions:
Some items that the player can carry can help or harm their ability to find secret rooms:
- Circinus reveals secret room sparkles for a certain amount of time upon entering a floor.
Secrecy makes it so that the sparkles will not show up even if they should.
Djinn is a familiar that will reveal secret rooms by snapping to create sparkles when the player enters a room with a secret room connection in it.
Secret Rooms can however be found without the aid of sparkles. It is a little bit more difficult but with some practice it can be almost guaranteed that the secret rooms on a floor can be identified without wasting a single bomb to find sparkles. Using the information on knowledge of connectivity of rooms, information about the size of room (some rooms are too small to have secret room exits) and texture clues it can be quite obvious where secret rooms are located.
Texture Clues
It is pretty difficult to cover all the texture clues comprehensively, usually the texture clues are learned intuitively over lots of practice but it is possible to look for specific clues in the textures to find secret rooms. Each zone has different texture clues due to the different wall textures.
Goldmines
The easiest texture to train people on in goldmines is the first North wall texture they see in the game, the wall texture is clearly repeated twice in the center and while that isn't always the only indication you need to look for it can be a good place to start when trying to learn how to find secret rooms based on only textures.
Oil
Oil does not light on fire if it is covering an entrance so if you have some Oil on the ground in front of a potential location for a secret room wall and you try to light it on fire and it does not light then you know you can bomb the wall and find a secret room. It is very rare to get this exact set of circumstance though.
This behavior is due to the developer's philosophy of wanting to guarantee that there is always a way to escape damage upon entering a room if you are good enough at the game and recognizing situations.
Tutorial Secret Room
The tutorial has a secret room, this is the only thing in the tutorial that is missable, and it is also an achievement to find it. (The achievement can be gotten simply by start a new save and finding the secret room within the tutorial.
Map of the tutorial with the secret room found and highlighted
Trivia
- If two explosions go off simultaneously in a room with a secret room attached, extra sparkles will generate
- The tutorial secret room is the only secret room that doesn't have a ? on the room in the minimap.