I'm posting some photos on Facebook and Twitter that show places that are featured in the book as they are today. The first of these was the Burlington Arcade, now a respectable (even posh) shopping arcade; in 1859 it was well-known as a place where men met prostitutes.
The second photo shows the famous seven dials sundial that marks the centre of what was, when it was built, rather a desirable development. By 1859, the place was an utter slum and the column had been removed because it was thought by the authorities that it provided a meeting place for the mob.
Here it is as described in my book:
We arrived safely at a little plinth that marked the centre of the neighbourhood. Here there had once stood a pillar with the seven sundials that gave Seven Dials its name, but the pillar was long gone. Only a few stones, too low even for a mounting block, remained in the middle of this square. Not that the area was square. It marked the spot where seven streets met. In whatever direction you faced, sharply angled buildings stabbed toward you. The effect was disorienting, for each street looked the same. Furthermore, at this confluence, all the buildings that the traveller found himself looking at were public houses. Only dirty street signs, high on the walls of the narrow roads, provided any clue as to the direction that you should follow.Today, of course, it's the centre of a very nice part of London and the sundials have been reinstated.