Approximately 1.5 million people use the Greenwich & Woolwich Foot Tunnels to get from one side of the mighty River Thames to the other. They are, however, somewhat taken for granted. Have you ever stopped to wonder at their existence? They are quite remarkable - there's not much else quite like them in London, let alone the UK. At a time when we're going through an arduous process of trying to work out what London's next crossing will be - thankfully it seems the wonderfully impractical Garden Bridge won't be it - we should take a moment to appreciate how curious and marvellous these two crossings are.