These apartments form an intricate labyrinth, which extends a foot or more in diameter from the royal chamber on every side. Here the nurseries and magazines of provisions begin, and being separated by small empty chambers and galleries, which go round them, or communicate from one to the other, are continued on all sides to the outward shell, and reach up within it two-thirds or three-fourths of its height, having an open area in the middle under the dome, resembling the nave of an old cathedral. This area is surrounded by large gothic arches, which are sometimes two or three feet high next the front of the area, but diminish very rapidly as they recede from thence, like the arches of aisles in perspective, and are soon lost among the innumerable chambers and nurseries behind them. All these chambers, and the passages leading to and from them, being arched, contribute to support one another; and while the interior large arches prevent their falling into the center, and keep the area open, the exterior building supports them on the outside. The interior building, or assemblage of nurseries, chambers, &c. has a flattish top or roof without any perforation; by this contrivance, if any water should penetrate the external dome, the apartments below are preserved from injury. It is never exactly flat and uniform, because they are always adding to it by building more chambers and nurseries: so that the divisions or columns between the future arched apartments resemble the pinnacles upon the fronts of some old buildings, and demand particular notice, as affording one proof that for the most part the insects project their arches, and do not make them by excavation. The area is likewise water-proof, and contrived so as to let the water off, if it should get in and run over, by some short way, into the subterraneous passages, which run under the lowest apartments in the hill in various directions, and are of an astonishing size, being wider than the bore of a great cannon. There is an account of one that was measured, which was perfectly cylindrical, and thirteen inches in diameter. These subterraneous passages or galleries are lined very thick with the same kind of clay of which the hill is composed, and ascend the inside of the outward shell in a spiral manner; winding round the whole building up to the top, they intersect each other at different heights, opening either immediately into the dome in various places, and into the interior building, the new turrets, &c. or communicating thereto by other galleries of different bores or diameters, either circular or oval.