Where do the tubes go?

It has come to my attention that a good chunk of the London Underground network does not exist on the weekends. This has been happening for the past 10 years at least. I am slow to recognise things.

So, the question is where do they go? On these weekends when the London Underground is not in London where does it go?

I have done some research and it appears that the London Underground is distributed over Europe. It appears that the Northern Line is deployed to Oslo where more trains run on the weekend and new stations appear. This could explain the abundance of Norwegians at Leicester Square and London Bridge. The Piccadilly Line appears to spend the weekends in Paris which explains the large number of French Players playing for Arsenal and the Circle Line seems to have occurred in Rome because the Italians like to visit many interesting places again and again. The District Line appears in Berlin for obvious reasons. The Central Line in Zurich for obvious reasons too. Other lines appear to oscillate between different countries.

This could explain why the London Underground invariably does not work well on Monday morning as it takes quite a long time to move the underground back again. It could also explain why it costs rather a lot. It's not easy making a mobile undergound system.