The chambers, which seem to follow no definite plan, are excavated in the soft limestone and arranged in two storeys connected by a staircase, part of which still remains in place. The finest rooms are in the upper storey. The largest is circular, and contains in its walls a series of false doors and windows. It is in this room that the remarkable nature of the work in the hypogeum is most apparent. On entering it one sees at once that the intention of the original excavator was to produce in solid rock underground a copy of a megalithic structure above ground. Thus the walls curve slightly inwards towards the top as do those of the apses of Mnaidra and Hagiar Kim, and the ceiling is cut to represent a roof of great blocks laid across from wall to wall with a space left open in the centre where the width would be too great for the length of the stones. The treatment of the doors and windows recalls at once that of the temples above ground. The mason was not content, when he needed a door, to cut a rectangular opening in the rock; he must represent in high relief the monolithic side-posts and lintel which were the great features of the megalithic 'temples' of Malta. Nor has he failed in his intention, for, as one moves from room to room in the hypogeum, one certainly has the feeling of being in a building constructed of separate blocks and not merely cut in the solid rock. No description can do justice to the grace of the curves and the flow of the line in the circular chamber and in the passage beyond it, and we have here the work of an architect who felt the aesthetic effect of every line he traced. Behind the circular chamber and across the passage just referred to lies a small room which, rightly or wrongly, has been called the 'Holy of Holies,' the idea being that it formed a kind of inner sanctuary to the chamber. It contains a rough shelf cut in the wall, and in the centre of this a shallow circular pit. It has been suggested that this pit was made to hold the base of the cult-object, whether it was a baetyl or an idol. This, however, is a mere conjecture. In the passage just outside the door of this room are two small circular pits about 6 inches in diameter and the same distance apart. They connect with one another below, and are closed with tightly fitting limestone plugs. In one of them was found a cow's horn. Their purpose is unknown, but similar pairs of pits occur elsewhere at Halsaflieni. In two of the largest chambers in the hypogeum the roof and walls are still decorated with designs in red paint. The patterns consist of graceful combinations of curved lines and spirals. Many other rooms, including the circular chamber, were originally painted with designs in red, which have now almost wholly disappeared. Many of the chambers are extremely small, too small for an adult even to stand upright in them, and their entrances are merely windows, perhaps a foot square and well above the ground.