▁castle ▁▁ ▁The ▁central ▁castle ▁was ▁originally ▁constructed ▁in ▁the ▁ 1 6 th ▁century , ▁but ▁heavily ▁re develop ed ▁in ▁the ▁early ▁and ▁middle ▁years ▁of ▁the ▁ 1 9 th ▁century . ▁It ▁compr ises ▁a ▁central ▁tower ▁with ▁three ▁bast ions ▁to ▁its ▁north - west , ▁north - east ▁and ▁south , ▁approximately ▁ ▁across . ▁A ▁cur tain ▁wall ▁with ▁gun ▁positions ▁originally ▁linked ▁the ▁three ▁bast ions , ▁but ▁this ▁was ▁substantial ly ▁alter ed ▁with ▁the ▁addition ▁of ▁walls ▁and ▁ch amb ers ▁to ▁produce ▁a ▁deeper ▁structure . ▁The ▁central ▁castle ▁forms ▁the ▁entrance ▁to ▁the ▁rest ▁of ▁the ▁fort ification ▁and ▁is ▁accessed ▁through ▁a ▁gateway ▁d ating ▁from ▁ 1 8 7 3 . ▁The ▁ 1 6 th - century ▁mo at ▁that ▁protected ▁the ▁castle ▁was ▁filled ▁in ▁during ▁the ▁ 1 8 6 0 s . ▁ ▁The ▁twelve - s ided ▁central ▁tower , ▁or ▁keep , ▁is ▁approximately ▁ ▁across ; ▁it ▁has ▁two ▁store ys ▁and ▁a ▁bas ement . ▁The ▁inside ▁of ▁the ▁tower ▁is ▁circular , ▁with ▁a ▁spir al ▁st air case ▁running ▁up ▁through ▁a ▁central ▁pill ar . ▁The ▁ground ▁floor ▁and ▁first ▁floor ▁rooms ▁would ▁have ▁originally ▁been ▁sub - div ided ▁to ▁form ▁living ▁qu arters ▁for ▁the ▁g arrison , ▁but ▁are ▁now ▁open ▁spaces . ▁Both ▁have ▁eight ▁em br asure ▁windows , ▁suitable ▁for ▁holding ▁l ighter ▁weapon ry ; ▁the ▁first ▁floor ▁room ▁was ▁sufficiently