Herodotus, The Histories -Extract- Labyrinth of Egypt

It has twelve courts covered in, with gates facing one another, six upon the North side and six upon the South, one after another. and the same wall surrounds them all outside; and there are in it two kinds of chambers, the one kind below the ground and the other above upon these, three thousand in number, of each kind fifteen hundred. The upper set of chambers we ourselves saw, going through them, and we tell of them having looked upon them with our own eyes. The chambers under ground we heard about only; for the Egyptians who had charge of them were not willing on any account to show them, saying that here were the sepulchres of the kings who had first built this labyrinth and of the sacred crocodiles. Accordingly we speak of the chambers below by what we received from hearsay, while those above we saw ourselves and found them to be the works beyond the human. For the passages through the chambers, and the goings this way and that way through the courts, which were admirably adorned, afforded endless matter for marvel, as we went through from a court to the chambers beyond it, and from the chambers to colonnades, and from the colonnades to other rooms, and then from the chambers again to other courts. Over the whole of these is a roof made of stone like the walls; and the walls are covered with figures carved upon them. each court being surrounded with pillars of white stone fitted together most perfectly; and at the end of the labyrinth, by the corner of it, there is a pyramid of 240 feet, upon which large figures are carved, and into this there is an underground way.

A labyrinth, with an underground level and an adjacent pyramid? That’s a megadungeon right here!