Ooh, shiny. I'd do that.

Isn't there a competition each year where people try and go to every tube station in the fastest time? So there must be a reasonable number of people interested in spending all day on the tube.

I have a book written by some Victorian adventurers who took a ship up to the Arctic Circle and came back down by sea and land. They were very silly people who took lots of tinned foie gras and thought it'd be more fun to go in summer when their route was nearly impassable. :)