ci, hi again.
One of the most rewarding pastimes for visitors to London, I think, is getting to know the tube. Or the Tube. And using it of course.
At every Underground station (if they haven't run out) you can pick up a handy-sized folded map of the layout of the lines and stations.
And of course, the map is everwhere handily shown, fixed to the walls.
The Tube is to me one of the Wonders of the World (Londoners, no comment necessary on its reliability, overcrowdedness and old-fashionedness. Foreigners, don't copy my English, it's crap
)
London is a six-dimensional city to me: three above ground, and three beneath. I know that's not very scientifically put, but still.
And to answer your question c.i., I expect Piccadilly Circus is on the Piccadilly Line, and so is Holborn. If we go there.
McT