Inaccessible Rooms

Within Undertale, there are various rooms that cannot be accessed through conventional means. These rooms cannot be accessed by changing the save data, as they will immediately redirect the player to a black room with a white dog. However, they still are present in the game data, and can be accessed in other ways.

Rooms are listed from the smallest number to the greatest number.

Room 123
Room 123, also known as room_water_prebird, is a room that is between room_water_farm and room_water_shop. It is a thin stretch of land that is surrounded on two sides by water. The path is covered in tall grass, which covers up an NPC that you can talk to. The NPC is never seen, but remarks about how they love to catch bugs in their spare time. They express disappointment, as they can only catch the same bug due to the lack of bugs in the underground. They will ask the protagonist to do something about their "friend", who they describe as having a creepy smile. If spoken to again, they will ask where the protagonist's "friend" went. There are exits from the area to the left and right, but proceeding through those paths crashes the game.

Room 264
Room 264, otherwise known as room_gaster is a room in which mysterious text appears in the Wingdings font style. Aside from this text, all there is is a black void. A distorted sound, perhaps Gaster's voice may be heard as the text progresses. A direct translation of the Wingdings text is as follows:

"ENTRY NUMBER SEVENTEEN DARK DARKER YET DARKER THE DARKNESS KEEPS GROWING THE SHADOWS CUTTING DEEPER PHOTON READINGS NEGATIVE THIS NEXT EXPERIMENT SEEMS VERY VERY INTERESTING ... WHAT DO YOU TWO THINK?" The last line is speculated to be referring to Sans and Papyrus, Toriel and Asgore, Alphys and Sans (since Sans is though to be linked to Gaster, and Alphys was the Royal Scientist following Gaster).

Room 272
Room 272, also known as room_water_redacted, is a dark room with nothing but a mysterious NPC in the middle. They fade away the further the player gets from them. When spoken to they will say nothing but the line * [redacted] in wingdings. This NPC is theorized to be W. D. Gaster. Leaving this room will bring the player directly to room 270, which is the sound test.

Room 273
Room 273, also known as room_water13, is an unused room that appears to be in the Waterfall area. It consists of a long, narrow pathway, which leads to a large, flat area of land that's covered in tall grass. Bridge Flowers can be found in the grass here, which can be used to reach a pathway on the right side. The exit to the right of this room leads to room 274, which houses nothing but a black overworld and mysterious red sprites.

Room 296
Room 296, also known as room_fire4, is an old room that seems to be in the Hotland region. It contains a path that goes up and then turns right, while being lined with steam vents the way through. Another Medium plays in this room. It is not linked directly to any other room.

Room 297
Room 297, also known as room_fire10_old, is an unused room that appears to be in the Hotland region. It contains a pathway with conveyor belts that must be traversed in order to get to the other side. The player can fall off of the conveyor belts, which will bring them directly to room 298. The door at the entrance will also bring the player to room 298. The exits at the left and right of the room do not bring the player anywhere.

Room 298
Room 298, also known as room_fire10A_old, is a room that appears to be in the Hotland region. It contains two platforms at each end of the room, linked by a path of conveyor belts. In the room, there is a single Echo Flower, which says nothing but "*Error!" One end of the room has a door which links directly to room 297, while the other end of the room has nothing but a bowl of dogfood. This same bowl can be found in Papyrus's shed.

Room 299
Room 299, also known as room_tundra_placeholder, is a room that appears to be in the Snowdin area. It consists of an ice puzzle, which has ice that will send the player backwards if touched. It does not link directly to any other room, and there is nothing on the other side upon completing the puzzle.

Room 300
Room 300, also known as room_ruins12B_old, is a room that bears noticeable similarities to room 13, in which Monster Candy can be found. In Room 300, however, Rock Candy can be found. You can only take one Rock Candy at a time; to take another, you have to either eat or drop any Rock Candy that is currently in your inventory. If you try to take another, it will be described as too heavy to take. The joke is that the candies are rocks and are too heavy to carry more than one.

Room 301
Room 301, also known as room_tundra_rollsnow, is a generally empty room consisting of nothing but a small snowball. This small snowball can be pushed, causing it to gradually grow in size until it reaches a set limit. This room does not link directly to any other room.

Room 302
Room 302, also known as room_water7_older, is a room that appears to be part of the Waterfall region. Entering this room without changing anything results in a crash; to avoid this, obj_waterpushrockgen must be edited or removed. This room houses a lone Echo Flower that says "*Error!", as well as several other flower-like objects. The tops of these objects combust upon interacting with them. Lighting up all of these flowers is supposed to activate a path on the right of the room. Leaving this room crashes the game.

Room 303
Room 303, also known as room_meetundyne_old, is an older version of the room in which Undyne is met. It has some NPCs from Snowdin and a sign which acts as an Echo Flower. It will repeat the last line of dialogue that the player has encountered within the room. It contains the scene in which Papyrus talks to Undyne, which consists of the same dialogue. After this event, Monster Kid's dialogue can also be seen, although they are nowhere to be found. The right exit of this room leads to room 304.

Room 304
Room 304, also known as room_water_mushroom, is a room in which one of the NPCs from MTT Resort is located. This NPC will ask what "outside" is like, and his response will vary based on whether you agree to tell him or not. He will ask the player to investigate the room to the right and inform him of what is in it. His dialogue can be compared to that of Ragel's, as he talks about being rooted to the ground and wanting to see what is outside of the room. Because of this, it is likely that this is the room in which Ragel was originally meant to be found, before being moved to Temmie Village. The bottom exit of this room links directly with room 303.