Why did the great hall of the warren become "The Honeycomb" in Watership Down?
The great hall of the warren becomes known as "The Honeycomb" because of the network of vertical roots that support the ceiling. These, in addition to a series of blocks of earth which are left untouched in the areas where there are no roots to hold the ceiling up, give the great hall the feeling of a honeycomb.
When Hazel and his band of rabbits discover the abandoned warren at Watership Down, they plan to add a "great burrow", a place underground where everybody can be together (to) talk and tell stories and so on". They base their plans on a similar room they had seen at Cowslip; Strawberry, who has joined them, is familiar with that room's construction. Strawberry notes the importance of the roots, telling the group that "they take a lot of the load...if it weren't for those roots the ceiling would fall after heavy rain". Hazel is disappointed to think that the room will be divided by the "several thick roots that go straight down" in the great hall, but Strawberry insists that "they shouldn't be gnawed through and taken out", because they will be needed if they are planning to have a hall of any size".
Strawberry assures Hazel that the rabbits will be able to "go in and out among (the roots)", and that "they won't hinder anyone who is talking or telling a story". Strawberry engineers the excavation of the hall himself, and when it is done, its honeycomb-like structure turns out to be functional and not at all unpleasant -
"At the north end, the beech roots (form) a kind of irregular colonnade...(giving) way to more open central space...and beyond, where there (are) no supporting roots, Strawberry (leaves) blocks of the earth untouched, so that the south end consist(s) of three or four separate bays (which) (narrow) into low-roofed runs that (lead) away into sleeping burrows" (Chapter 20).