In a vast network of tunnels carved into the rocks under the Maltese capital Valletta, faded maps of the Mediterranean hint at the place’s role in directing key battles in World War II.

Malta is now restoring the 28-km (17-mile) of tunnels, planning to open a huge section to the public.

The compound, hidden under the picturesque port city perched on cliffs above the sea, was built by the British and served as the staging ground for major naval operations. The British military withdrew in 1979 and the compound was abandoned for almost 40 years.

German and Italian forces bombarded Malta intensively between 1940 and 1942 to try to gain control of the Mediterranean, but did not manage to force the British out. During the Cold War, the tunnels were used to track Soviet submarines.

Over the years, water and humidity have let rust and mold spread. Some rooms have been vandalized, but traces of the military apparatus that once occupied the complex still remain. Military cot beds, tangled cables and dust-covered rotary phones litter the rooms.

The Malta Heritage Trust, a non-governmental preservation group, began the multi-million dollar restoration of the site in 2009.