If you hit the flat lands between London and Peterborough you would have been in the Fens (low lying marshland around Ely and Cambridge, it's mainly farmland and originally was drained using the polder system - hence the drainage channels - locally known as dykes). I used to work in Cambs and lived out in the Fens for a short time in a place called Manea - your train would have taken you through the village - if you'd have done this journey in the winter when they flood the fields you would have travelled for some miles on an embankment with nothing but water on either side of the tracks.