Labyrinth - Blackfriars

This is Mark Wallinger's Labyrinth at Blackfriars underground station.

Eventually every one of the 270 underground stations will have a piece of art like this. Each labyrinth is unique.

As far as I can tell, around 230 have been installed so far, though even when you know a station has one it can be hard to find as it could be in the ticket hall, on any of the platforms, or in any of the connecting tunnels.