Ambrus is now Master of the Labyrinth. As long as he wields the Spear of Theseus he can open any doorway into a portal to the Labyrinth and enter it. Once in the Labyrinth he can travel d6 hours and attempt a will save, DC15, to open a new portal to wherever he wants to go.
Alternatively he can travel 3d6 hours and find the nearest available Labyrinth exit automatically.
Additionally, while in the Labyrinth, Ambrus (and companions up to his mythic tier) can survive without food or water, although sleep is still required.