The subterranean chamber (O) is about 46 feet long and 27 feet wide, but is extremely low, the ceiling varying in height from a little over 3 feet to about 13 feet from the rough and apparently unfinished floor. From the south side of the subterranean chamber a low tunnel runs about 50 feet and then meets a blank wall. These constitute the only known openings in the Pyramid, with the exception of a few niches, exploration holes, blind passages, and the rambling cavernous tunnel (B) hewn out by the Moslems under the leadership of the Prophet's descendant, Caliph al Mamoun.