The Palace Beyond

From publisher blurb: The Palace Beyond is an OSRIC module designed for 4-6 adventurers of levels 6-9. The Palace Beyond is ancient, and the race that built it is long gone. The palace exists on many levels of reality, and it is said it is everywhere and nowhere at once. It connects different parts of the world: it is possible to walk through a magic portal, into one of the palace’s corridors, turn around a corner, and then walk through another portal to end up in a far away land. But now the palace is deserted, and the magic that made it possible is slowly crumbling. Its pocket dimension is collapsing, and large sections of the palace have already fallen into Nothingness.