My first encounter with this was on a foggy November morning, and I had no idea what was going on.
There's another very similar but smaller one at Heathrow, next to the Hatton Cross tube station. That one has the added attraction of London taxis and Ubers traversing it at high speed.
There's another very similar but smaller one at Heathrow, next to the Hatton Cross tube station. That one has the added attraction of London taxis and Ubers traversing it at high speed.