 The blockhouse overlooks the sea and the estuary from its position on a rocky outcrop . It is surrounded by cliffs and a curtain wall , enclosing a semi @-@ circular area around 500 square metres ( 5 @,@ 400 sq ft ) in size , incorporating slits for firing muskets . A rectangular bastion , 5 @.@ 7 by 3 @.@ 2 metres ( 19 by 10 ft ) internally with 0 @.@ 75 metres ( 2 ft 6 in ) thick walls , protects the rear of the blockhouse . The original pathway to the blockhouse was blocked by later work , and the current steps up to the building are of 19th century origin . 
