[@Aisling] That'd be cool!

Where I live at, there is a castle that has got a secret passage underneath it. When you go to the basement, you can see a part of it through a glass window. Historians have tried to crawl it, but parts of it were either bricked or collapsed, so they couldn't reach the end. Nobody knows how long it is or where it ends, but there is a legend that says that it leads to another castle, about 30 kilometers away from 'ours'. 

I've also heard that many castles have got something like that. During sieges, people used them to flee, and for food supply.