In 1968, based on the guiding strategic principles of combined offensive and defense and the requirements of combat missions, the ROC Armed Forces excavated tunnel docks that could accommodate small boats at Nangan, Beigan, Xiju, and Dongju, designating the plan “Project Beihai” (North Sea). Nangan’s Beihai Tunnel, also called the “underground port,” has a layout like井, and can hold 120 small craft. Ten minutes’ walk from the tunnel is a model military stronghold; there are three levels of tunnels inside, with complete military facilities inside. In February 2007, it was opened up as a new attraction connected to the Beihai Tunnel. The Iron Fort (Tiebao) lies to the west of Renai Village, below Binhai Road towards Jinsha. This was originally a separate rocky shoal jutting up out of the sea, but for strategic purposes, the Armed Forces hollowed it out and covered the top with concrete to serve as a stronghold standing unyieldingly against the crashing waves around it. Shards of glass were inserted into the nearby rocks to protect against frogman infiltrators from the mainland. Although the Iron Fort has been abandoned, everything has been preserved- the underground stone rooms, tunnels, loopholes, gun batteries, and other defenses are all as they were. This was where the only dog (an alsatian) with military rank ever to serve on Matsu was based. Once an important strategic strongpoint, it is now open to visit for free all day, and is a great place to get a taste of the wartime atmosphere of years past.