The barracks was intended to house soldiers to guard the dock. It was made with a thick, bomb proof wall in case of attacks. When the island was converted to a prison, the barracks was turned into apartments for the families of correctional officers. Tours to the island are catered by boat going there every 30 minutes. You'll be briefed by the island guide as soon as you arrive at the dock. Get yourself a free brochure found in front of the souvenir shop to guide you personally as you explore the island yourself.