sounds interesting. I've always been intrigued by tunnels, and allthe other stuff that you cannot see that's beneath us.
Up in Washinton DC they are having problems with sewer gas explosions blowing manhole covers off. In the old sewers, the electrical lines were run through them on top. The sewage also flows through them on the bottom. Because both share the same line, it causes trouble. Because of the sewage, they fill with sewer gas. When an electrical problem develops, like a spark or something, it will ignite the sewer gas causing a massive explosion that blows manhole covers off in the streets, and even forcing water back up through toilets and drains inside peoples' homes. I hope I'm not down in a sewer when something like that happens, but it is cool when you can observe it happening from the street level.
