Inside the vaulted dome is a stone pillar some 12ft/37m high, which would have supported a revolving ladder used to reach the nests lining the walls.
Y tu mewn i’r gromen mae piler carreg tua 12 troedfedd/37m o uchder, a fuasai’n cynnal ysgol gylchdro a ddefnyddid i gyrraedd y nythod ar hyd y waliau.