fastness

1. N-COUNT A fastness is a place, such as a castle, which is considered safe because it is difficult to reach or easy to defend against attack. 要塞; 堡壘[文學性] [with supp]

They could have withdrawn into the mountain fastness of Eryri. 他們本來可以撤廻到艾瑞的山區要塞裡。