Knock-Knock Doors are in every street, but not playgrounds. They are special doors that don't allow entrance, but tell knock-knock jokes!
Examples of them include;
- Knock Knock. -Who's There? Kent. -Kent who? Kent you tell?
- Knock Knock. -Who's There? Noah. -Noah who? Noah don't know either.
Some place have hidden knock knock doors, accessed by glitches. But if they still exist in ToonTown Rewritten is still currently unknown.
Also, when the building connected to the door is turned into a cog building, the cog's enter and exit what used to be the knock knock-door. After the building has been recovered, either the cogs produced from the building with fly away, or they will walk back into the knock knock door, although it is no longer a cog building. That would be quite a sight!