Quake: Dawn Of The Machine - Secret area in Veils of the Old One

At the end of In To The Abyss Of Time, behind the exit, there is a ring to switch dimensions. When you take it, a message pops up: "You Disabled a Trap".

If you take it, in the next level Veils Of The Old One, when you take the teleporter room guarded by 2 grunts, instead of taking you in a spike room with 2 ogres, it takes you to a totally different location (some kind of floating structure).