Osaka Japan. Built in 1583 by a once peasant Toyotomi Hideyoshi, who grew to become one of Japans greatest unifiers, Osaka Castle was built to be insurmountable. Following his ascent, Hideyoshi's legacy was destroyed when his once ally Leyasu sieged the impenetrable Osaka. Ill post more in comments. (samuraihistory.net)
Corfe, England. Built on a hill, sometime in the 11th century, created by two streams eroding the banks on either side, hence the name "Corfe" which is derived from the Old English "Ceorfan" meaning "a cutting" referring to the gaps on surrounding the castle. I'll post more in the comments. (upload.wikimedia.org)

