One particular bit of the 'Thud!' book is the hint (Well, it's pretty obvious) of Anhk-Morpork getting an Underground Train system. (One of the Devices can turn for invinity, if needed, and the sign on the entry to the Mine in Anhk-Morkpork was a circle with a line thought it: Which is the sign for the London Underground.) It's interesting to see what Discworld is slowly turning into. It isn't as much a fantasy world of dungeons and dragons, it's a parody of our world.