Epping is now the terminus of London Underground's Central Line. The line used to continue beyond Epping, through Essex countryside to Ongar. The line to Ongar closed in 1994.
This image, taken a short distance beyond the Epping terminus, shows traces of this line having once been part of London Underground. The Underground uses a third- and fourth-rail electrification system, with the fourth rail being in the centre of the tracks. Although the third and fourth rails have been removed here, the insulation pots which carried them, both in the centre and on the right-hand side of the tracks, are still there.
A preservation society has been established to operate trains on the Epping to Ongar Railway. Their website is here:
Link