The enigmatic House of All Worlds is inhabited by Lady Alvane and a much older Crow. Its exact nature and location are still unknown, although Lady Alvane describes it as neither Stark, nor Arcadia: "this place is Between, and Everywhere." It is visited at the beginning of the story by two guests in rustic clothing who have come to hear Lady Alvane tell them a story.
April reaches the House of All Worlds when she is being pursued by Vanguard agents, via the "Mystery Door" outside the Fringe Cafe that opens some kind of portal. April says that it "felt different, not like Shifting." Lady Alvane tells her that, while April brought herself there, Lady Alvane opened the door for her.
Lady Alvane and Crow refer to the reunification of the worlds as having already occurred, but pre-reunification April is able to visit, so there is some kind of time paradox. Lady Alvane tells her guests "There are enough fairy tales in the worlds already", implying that the House of All Worlds is not the sole remaining world following reunification.