Plane Shift

[Felix]

...ahem...

Yeah. Or that.

...maybe...

 

[Pyrex]

Dimension Door and Teleport don't ever allow you to change planes... They just move you around the plane that you're currently on at the moment.

Correct, DimDoor and TP don't allow you to change planes, but as both spells work by creating a shortcut through the Astral Plane, if Graybeards PC's were on a demiplane that was sealed off from the other planes, lack of access to the Astral would prevent both Dim Door and TP from functioning.