Down the tubes.

 Here is a brief update to the upside down tube map post I did a year or two ago. You can read it here if you're desperate.

There is a guy who talks about tube stations on Youtube, its quite informative and there is a video about why there's hardly any tube down south.

Turns out that we have really bad soil and a proliferation of train lines that take over most of south London in a way that they don't up north.

The soil bit is interesting, as a kid I can remember it being quite a lot of sand and oyster shell material in a bank at what would become my current workplace. You can see what it was like in the wiki link posted and how its not really suitable for tunneling and such. Though the DLR at Woolwich seems to manage OK, I guess modern methods help.