Corregidor Island had a vast network of tunnels built under solid rock. The Americans designed Fort Mills solely to ward off attacks from the sea but they soon realized that it would be very vulnerable to attacks from the air. So in 1922, the U.S. Army Corps of Engineers, with the help of the Philippine Scouts and a thousand convicts from Manila's Bilibid Prison, began work on tunnels that were meant to be a bomb-proof storage and personnel bunker. Its main tunnel was built under Malinta (full of leeches) Hill and the tunnel complex came to be known as Malinta Tunnel. It was finished in 1932.
During the Battle of Corregidor, Malinta Tunnel served as the headquarters of General Douglas MacArthur and was also the seat of the Philippine Commonwealth government under President Manuel Quezon (you've seen him before here) and Vice President Sergio Osmeña. Today, the main tunnel is the venue of an audio-visual show about the siege of Corregidor. With a script written by National Artist for Theater and Film Lamberto Avellana and sculptures made by National Artist for Sculpture Napoleon Abueva, the show is a must-see for WWII history buffs and for anyone who would like to understand what so many men and women had to endure for our freedom. (Please pardon the fuzzy picture. It was the best I could do in the darkness without using a flash.)
The main tunnel had 24 side tunnels branching from it. Much narrower and lower than the main tunnel, it was actually these laterals that served as storage areas and headquarters. Some of them led to other entrances, and two of the tunnels led to their own tunnel complexes. One of these was the underground hospital which had 1,000 beds. The main tunnel was restored for the lights-and-sounds show, but many of the smaller tunnels collapsed during WWII and remain that way.
Back outside, the island is also riddled with tiny tunnels and caves. I forgot to ask the guide if these were connected to the Malinta Tunnel complex, but he said that they were used by both American and Japanese snipers.
CORREGIDOR ISLAND SERIES #3 OF 7