Secret Room under Snowbound

When playing Halo 3's Multiplayer map Snowbound on Forge, it is possible to glitch through the ground into a blue room hidden underneath a glass floor inside one of the bases.

Instructions (Turret Method)
To perform the glitch, a player must first overload the map with Trip Mines.

From there, they (Person A) must go to the base with a room under the floor. They will need to bring a friend (Person B) with them. The two will perform a variation of the Forge Turret Glitch.

Person A, in Edit Mode, should spawn a Plasma Cannon or an Machine Gun Turret and set it down. Person B, in Player Mode, should man the turret. At this point, Person A should grab the turret and turn it sideways, such that Person B is in between the turret and the floor. At this point, Person B should enter Edit Mode; they will find themselves beneath the glass.

Respawn Points can be placed in the room.

Instructions (Teleporter/Host Method)
This method requires two players to cooperate over Xbox Live; the two players will need to figure out which one of them is the "host".

First, the two players must overload the map. Then, the glitch may be attempted.

The player that is not host should spawn a Receiver Node and place it on the glass floor. They should then button-mash A until the Teleporter sinks beneath the floor. Once that is done, the player can spawn a Sender Node and use that to get in. This method works in other parts of Snowbound, including the Ghost/Mongoose spawn point.