#862 Corregidor Island, Philippines

http://en.wikipedia.org/wiki/File:Map_of_Corregidor_1941.jpg

At the entrance to Manila Bay is a strategic island shaped like a tadpole, that has been fortified by everyone who has controlled the Philippines: first the Spanish, intermittently Chinese pirates, Dutch sailors (1647), and British soldiers (1762), then the Americans, ending with the Japanese during World War II, before they lost the war.  

Surrender of US troops at Malinta tunnel in May 1942
http://en.wikipedia.org/wiki/File:MalintaSurrender.jpeg

Approximately 6km long, it was named because it translates as "to correct" because Spanish used it as a customs port for "correcting" documents. Later, it was known as Fort Mills by the Americans, and had several facilities for officers, a 1 mile long barrack for soldiers, a small airfield, as well as the all important lighthouse from 1853 onwards. It was incredibly important for both losing and gaining the Philippines to the Japanese invaders during World War II with brutal battles May 1942 and January 1945 respectively, being the losing battle when the Japanese blocked Bataan from supplying them with food and fresh water and one of the first to be liberated. It was very heavily bombarded and its ruins remain a memorial to the many that died during the war, with several memorials to Filipino and American solders and a Japanese Garden of Peace.

http://en.wikipedia.org/wiki/File:Malinta_tunnel_diagram.jpg

http://en.wikipedia.org/wiki/File:Malinta_Tunnel.JPG

One of the most fascinating military constructions was the Malinta tunnel, under the almost 600m high volcanic peak (Filipino scientists believe that despite erupting last around a million years ago, it could still be an active volcano). This was, impressively, the temporary location for the government of the Philippines (Dec 1941-Feb 1942), and it was outside this tunnet that Manuel L. Quezon and his Vice President Sergio Osmena were inaugurated for their second term as leaders of the Philippines Commonwealth. General Douglas MacArthur also made it his headquarters after much of the Philippines was controlled by the Japanese.

The ruins of the mile-long military barracks.

If ever a military base has been respectfully converted -- this is it. It is a peaceful, historical museum of an island now, with beautiful greenery and few visitors, the circular guns no longer used and the roads only for tourists.
Source: http://en.wikipedia.org/wiki/Corregidor_Island
http://en.wikipedia.org/wiki/Malinta_Tunnel
http://en.wikipedia.org/wiki/Fort_Mills