"You are entering the vicinity of an area adjacent to a location.
The kind of place where there might be a monster, or some kind of weird mirror.
These are just examples; it could also be something much better.
Prepare to enter The Scary Door."
Futurama
And the original behind The Scary Door:
"You're traveling through another dimension, a dimension not only of sight and sound but of mind.
A journey into a wondrous land whose boundaries are that of imagination.
That's the signpost up ahead - your next stop, the Twilight Zone!"
Or:
"There is a fifth dimension beyond that which is known to man.
It is a dimension as vast as space and as timeless as infinity.
It is the middle ground between light and shadow, between science and superstition, and it lies between the pit of man's fears and the summit of his knowledge."