The south half of the seemingly solid base of this building is honeycombed with at least nine rooms interconnected by sloping passageways and interior stairs. The inconspicuous entrance is on the south side of the base, near its east end. The rooms are small but astonishingly high for their area, in some cases reaching almost 27 feet in height. Their purpose is not well understood: they are pitch black and it seems unlikely they would be useful for storage. There may have been similar rooms on the north side, but none have yet been found.
In 1971, a narrow passageway and stairway were discovered in the north tower. David F. Potter notes that the passage is now blocked by masonry debris but apparently led up to an exit on the roof level of the building between the towers.