A room link is a number that specifies which room is attached to another room. Each room has four room links: left, right, up and down. If the prince leaves room 2 to the right, and the right room link is set to 19, he will enter room 19 from the left. If the level uses regular room links, room 19 will then have its left room link set to 2. This way, if the prince leaves room 19 to the left, he will end up back in room 2.
Sometimes a level contains one or more broken room links.