Which of London Underground's line's go deepest underground?

Question

Which of London Underground's line's go deepest underground?

Answer 1

The Underground's deepest point below ground level is at Holly Bush Hill, Hampstead, 67.4m (221 ft)

Answer 2

The Northern end of the northern line.

Answer 3

That is not as easy as it sounds because there is no public information available about the depth of the lines between stations. The deepest station is Hampstead at 191 feet below street level.

Answer 4

The one marked "deepest London Underground line"... just a guess.

Answer 5

Sad but true fact, only 47% of the underground is actually underground.

Answer 6

Hampstead Station (at the north end of the northern line, as previously stated) is the deepest station at 192 feet below ground level.

The deepest point is close by at Holly Bush Hill (how ironic) which is 221 feet b.g.l.