Mysterious tunnels to secret places

I love stories of mysterious places. Combine that with dark tunnels and you could interpret that in a Freudian way or you could just go to this paranormal site for a great round up web sites devoted to secret and spooky tunnels:

There is something fundamentally and primally mysterious about caves and tunnels. Maybe it's their darkness or the fact that they open into the very body of the Earth. They are invariably the subjects of adolescent adventure stories, such as the Hardy Boys, Nancy Drew mysteries, and R.L. Stine's books. And they serve as backgrounds in exciting stories directed at older audiences as well, such as Jules Verne's A Journey to the Center of the Earth and the Indiana Jones films. Tunnels represent the unknown and touch the fears that reside deep in the primitive human subconscious. Recently, I've come across several sites on the Web that tell what some believe are true stories of vast underground networks of tunnels. And they are no less mysterious and fantastic than those used as settings in the fictional tales mentioned above. It's not that the tunnels merely exist and are unknown to most people, it's what they contain, who built them, and why - and that takes us into the deepest recesses of the unknown.