The Tuppenny Tube
Starting life early in the 1900s as the Tuppenny Tube (any ticket was a flat rate of two old pence), the Central Line is still pretty important. Beck's first version of the Tube map used the Central Line as the horizontal anchor, a role it maintained until the 1990 revision which diverted it at Bank Station to make the new DLR and older Monument Station links more prominent.
The line extends westwards to North Acton Station, where the line splits between west to Ealing Broadway Station and north-west to West Ruislip. Eastwards takes you towards the Essex stations of Epping and Hainault (via Newbury Park). The run from Ruislip to Epping is the longest non-stop section on the Underground; it takes an hour and a half to travel this section in full.
Sections of track near Bethnal Green Station are amongst the worst in the London Underground network resulting in some of the noisiest trains around. The signalling frequently breaks down resulting in confusion and delays all round.
To the East the Central Line goes through Liverpool Street Station, Bethnal Green Station, Mile End Station, Stratford Station, Leyton Station, Leytonstone Station. Leytonstone Station is on the border between zone three and four, and is also the last station before the split with some trains going to Woodford then Epping, and some to the Hainault loop, which eventually goes to Woodford.
Historical note: There used to be a small separate section of Central Line, which ran a shuttle service between Epping and Ongar, with intervening stops Blake Hall and North Weald. This section closed in 1994.