Secret Room under Snowbound
From Halopedia, the Halo wiki
This is a tutorial of how to get into the Blue Room Under Snowbound.
Overload the map by spawning 4 Trip Mines and setting the minimum respawn time to 4 seconds and keep using them until the first one runs out of time and blows up (These aren't necessary).
Go to the base with a room under the floor.
Get a friend there too. Spawn a Human or Covenant turret and make him go on it.
Then lift up the turret with him on it and turn it side ways and move it down and make the friend go into Edit Mode. Congratulations, you are in the blue room. You can also put respawn points in it.
One side will be a bright, "blue room", the other will be a scary, dark "black room".
There is also another way of doing this that has to be done with a friend on Xbox Live. You need to not be the "host". You can figure this out by using the Connection Host Method or you may already know it. First, it needs to be in Forge mode. Have the person that is not the host spawn a receiver node Teleporter, and place it above the glass floor. This person needs to keep pressing the A button until the teleporter is pushed literally through the ground. Once it is under, spawn a Sender Node and you can get in. This also works in other places on Snowbound, including the Ghost/Mongoose spawn point.
