there's an elevator with "1", "2", "3","K", and "M" because those are the "numbered" releases of Sonic games, which means a few things: 1-3 are expected, K stands for Knuckles and M for Mania, the significance of the elevator means "it's the next level", and the most hilarious, 4 does not exist in the chronological order of Sonic; it shall now be dubbed as, "Sonic's Return to Green Hill Zone."