Well known as the major sea defence for Manila Bay, which the Japanese (as they did to the Brits in Singapore with Sentosa) initially avoided.
The WW2 artifacts and ruins are a testement to the fury of the attacks and defense, and should be on everyone's must see attractions.
Sun Cruises out of Manila run day trips, and overnight packages.
Bangkas can also be hired from Marivelles, at the tip of Bataan.
Here is a good link - http://www.margarita-station.com/corregidor/ABC/abc.html
and for detailed history - http://en.wikipedia.org/wiki/Battle_of_Corregidor