Easily the most complex entity setup I have ever done.
Stepping on a tile (which is a door) triggers the doors representing the tile to change rapidly, making it appear it has happened instantly.
The door trigger for that trigger is then disabled, and a teleport trigger is enabled. If the player steps back onto the tile, all tiles are reset blue and you are teleported bact to the start. All teleport triggers are disabled, and the door triggers are enabled again.
There are 29 tiles in this example. There is a math_counter with a max set to 29. On the opening of a tile, it adds 1 to the counter, and the door opens when it hits its max of 29. 1 is subtracted from the counter when a tile is closed.
Each tile, when opened, triggers the opening sound. The sound is the actual sound recorded from the game, put through a crapload of filters to get rid of the background music. The counter triggers off the sound of the door opening, which has been converted from a midi I found on the web. The background music is the same. (This is also the first time i have use cue points in wav files.)
There are small clip brushes in between tiles to force the player to walk in straight lines. (Also to prevent cheating by walking on the edges of tiles and missing the triggers.)
When the puzzle is solved, all teleports and door triggers are removed from the map. The clip brushes are all one door, and are raised when the puzzle is solved also.
The background music can be turned on and off with the button near the spawn.
Credits to Talia from IRC for the math_counter idea, and to Nintendo for the music and idea.