20 (Mostly) Inconsequential Random Secret Rooms for Your Dungeons

I have a player who obsessively searches for secret doors, but I rarely ever include them. In order to occasionally give him something for his efforts, I’ve created the following list of secret rooms that he can stumble across without (immediately) derailing the campaign. These are ideally dropped into a traditional man-made dungeon or maybe a weird haunted house.

1. A cramped cell, only containing a skeleton shackled to the wall. The skeleton is humanoid, but there are three eye sockets in the skull. 
2. A small room with claw scratches on every surface (walls, floor, and ceiling). A small hole is bored into a surface does not connect to any other location in the dungeon. Whatever was in here is now long gone.
3. This chamber contains an elaborately painted circle and triangle painted on the floor in white. Melted down candles outline both shapes. There are scorch marks on the floor within the triangle. 
4. This room is filled with shelves of books. Most of the books have completely rotten away, but a few remnants can be found. All are written in a rare or dead language and are clearly of an occult nature. 
5. This circular chamber is only 10’ in diameter. Small gemstones have been embedded into the low ceiling as to replicated the constellations appearing on the winter solstice. The gems are very small and not expertly cut. They value 100 gold if all collected. 
6. This camber is barely large enough to contain a small table, on which are several black mirrors, each about 6” across.. With a successful magic check, a character can use one of the mirrors to remotely view a random room in the dungeon, much like a security camera. The mirrors lose their enchantment once they have been removed from the room. 
7. A hidden closet with a small chest with a simple lock. Inside are 1d100 x10 gold pieces. 
8. The walls are lined from floor to ceiling with small drawers, each one containing a tray of expertly preserved insects. Each tray can be removed and is worth 25 gold to an interested buyer. 
9. This small room is empty with the exception of a 1’ diameter hole in the center of the floor. A foul odor and strange noises gurgle up from the hole.
10. When the door to this secret room is opened, a torrential wave of (see below) pours out. Once the wave passes, there is only a wall behind the door.
1. Tiny frogs.
2. Wet, frantic rats.
3. Blood
4. Ice-cold sea water
5. Fingernail clippings
6. Wine
11. This room contains a writing desk and several drafting tools. A dungeon map is painted onto the wall above the desk. It is not a map of the dungeon the players are currently in. 
12. This secret door opens up to a hallway that seems to stretch endlessly into darkness. Eventually, the hall begins to curve in a wide arch. The characters will eventually find a room at the end of the hallway. In a pointless display of spacey-wacey magic, this room is the same room from which they entered the hall.
13. Nothing is in this room other than a chair bolted to the ceiling. 
14. A 10’x20’ room with an ornate sarcophagus laying in the center. There are very obvious hinges and handles to open the sarcophagus. Players who use their hands on the handles to lift the lid will trigger a trap that will slide a small razor along their fingertips. The blood drawn from this trap will flow into the sarcophagus, awakening the ancient vampire inside. Should the lid be opened any other way, a desiccated body will be found within. Only introducing blood to the body will restore the vampire. 
15. This small closet contains a dusty collection of various knick-knacks. All of the items are imbued with pointless magical auras. One of them is a lich’s phylactery. 
16. This large chamber is empty with the exception of a statue of a beautiful figure, enshrouded a dusty canvas. 
17. A torture chamber with a drain in the floor and a chute that leads to a chamber filled with bones. Rusty shackles hang from the ceiling and tools of torture are scattered along the floor.
18. This room contains a pool of black oil, only an inch deep, 20’ in diameter, with only about 3’ to walk around the pool.
19. A small closet with a single lever on the wall. When activated, there is a loud, grinding noise. It doesn’t affect anything in the dungeon, except maybe rile up some monsters. 
20. On the other side of the secret door is a wall, on which is drawn another door in chalk.