From the kickstarter page for Lords of Gossamer and Shadow
Jason Durall pointed out.
Bridging Doors. While Wardens are limited to Doors that lead to-and-from the Grand Stair, Masters know how to connect two doors in a single Gossamer world together so that they are directly linked, opening from one to another. To do this, the Master must be physically present at one of the doors to be linked (which must be closed) and concentrates on the other door to be linked. This can take a few minutes, less so with a strong mental impression of the other door, and even less with a direct psychic or magic link to the other place. These doors only open from one door within a Gossamer world to another place on the same Gossamer world. They can never bridge worlds.
Bridged doors lack the invulnerability of Doors on the Grand Stair, and they can be accessed and affected by any Warden or Master. These bridged doors are rarely permanent, and the duration will last only so long as the Master desires, usually a matter of days. Making a permanent bridge between two mundane doors takes considerably longer, a process measured in days rather than minutes.
This ability needs some thought, it can be powerful enough to break a lot of scenarios a GM might normally organize.