After settling in Macao, the Portuguese began to construct fortifications and defense works of varying scale across the city, like the city wall and fortresses. The military structures (tunnels and fortifications), armaments and military training for soldiers in Macao were modernized with the advent of industrial revolution and modernization. A club was set up for servicemen and a military-themed museum was built. Over the centuries, Macao is left with plenty of military sites whose layout and features are less known to outsiders since military issues were treated as highly confidential in the past. Today, we can embark on this journey to unravel the hidden secrets behind these military facilities.