How Green Park works

"What on earth is this horrendous tunnel for?" you sigh to yourself, as you once again make the mistake of changing between lines at Green Park. In an effort to figure out exactly how bad interchange here is, I've done a few laps of the station and come up with this diagram.

It turns out interchange between the Jubilee and Victoria is perfectly reasonable, but anything involving the Piccadilly Line sends you down one of the long tunnels. Changing between the Victoria and the Piccadilly you can avoid a long walk by going up to the ticket hall and back. But between the Jubilee and the Piccadilly a long walk is inevitable and you should avoid journeys that need it (unless you need to use lifts, because then it's the only interchange you can do here). The Jubilee Line is also long trek from the street.

A few notes: I used the Green Park drawing from here as a starting point, so while the Piccadilly and Victoria lines are likely to be accurate the Jubilee Line location is pure guesswork. The parallel grey lines are escalators, the stripey bits are stairs and the black squares are lifts. If it isn't obvious, all escalators go down in the direction away from the ticket hall.