This is very interesting (apologies if an ad starts auto-playing; I’ve taken to preemptively muting my speakers whenever I hit the Daily Mail):

Daily Mail – Going underground: Mile after mile of ornate brickwork and labyrinthine tunnels which reveal the beauty of London’s hidden River Fleet

In true tabloid fashion, the photos are lifted from Flickr and the fun facts within the article are probably lifted from Wiki or something, but anyway it’s very interesting. For instance:

One of the tributaries of the Fleet was called the Holburna (‘hollow stream’) by the Anglo-Saxons, from which we get the name Holborn.