The riddle
Where Does One Wall Meet the Other Wall?
The meeting place
Two walls of a room join at a corner, the place where two surfaces or edges meet. That is the literal answer. It is also what a person says when arranging to see a friend: "meet me at the corner". The riddle gets its charm from the way the plain answer and the everyday phrase line up.
The talking walls
This question is a close relative of a well-known joke: "What did one wall say to the other wall?" The punch line is "I'll meet you at the corner." The joke gives the walls a voice, and the riddle asks about their position. Both end at the same place. It works well as a dialogue, with one person playing each wall and the second answering the first.
Counting in a square room
A square or rectangular room has four walls and four corners. Each wall has two ends, and each corner joins two of those ends, so four walls with two ends each make eight ends, shared in pairs, which gives four corners. Each corner of a rectangular room is a right angle of 90 degrees, and four of them add up to 360.
A room without corners
A round room has one continuous wall, and no two walls meet, so the joke cannot be told there. A related puzzle about round shapes is the question of a circle's sides.