In the depths of the Red Cathedral in Mechanicsburg is the mysterious artifact known as the Monolith. Under normal circumstances, this device allows for instantaneous transport between it and a similar mechanism/gateway located at a remote location; one such connection is located in The Refuge of Storms, and there have been hints that other such sites exist elsewhere. (See below.) There is also a distinct impression that the Monolith is older than the Cathedral that now surrounds it; it is unknown if said Cathedral was intentionally built on top of it.
Well in advance of our heroine Agatha Heterodyne coming into power over Mechanicsburg, at least one faction of the organization called The Knights of Jove was aware of the existence of the Monolith and knew how to operate it; how much further this knowledge has currently (re-)spread is also unknown. During the Siege of Mechanicsburg, two members of The Storm King Conspiracy, The Abbess of the Red Cathedral and Martellus von Blitzengaard, attempt to take a kidnapped Agatha through the Monolith gate; following a jumbled melee in the Monolith chamber, Agatha, Tweedle, Violetta, Krosp and a solitary Wasp-Eater are the ones who make the jump.
Because they all do this at the exact moment which Klaus Wulfenbach activates his time-freezing "Take Five" device, the trip, still subjectively instantaneous for the travelers, takes two and a half years as far as the rest of the world is concerned. This event is referred to by Girl Genius fans as the Timeskip. The effort of retrieving/accepting eventual arrival of this group the The Refuge gate to explode; the status of the Mechanicsburg Monolith is, yes, unknown.
A Wider Connection Edit
Upon (eventually) being told how Agatha escaped Mechanicsburg, Zeetha immediately makes a to a piece of Skifander lore, "Queen Luheia's Mirror", a magic gate that the first Skifander inhabitants evidently used to originally travel to their far-off home. Unlike the Monolith, the Skifander Mirror has long been dormant. Later still, Queen Albia of England that she too is in possession of a non-functional Mirror. Meanwhile, in the side-story Homecoming King, it is indicated that the original Heterodyne used the Mirror network, or something very similar, in his conquests of chunks of The Known World.