Epping station is the place you're thinking of, the end of the central line.
Come off the M11 at J7 and follow signs to Epping, around 3 miles or so from the motorway,and the station's not hard to find -be warned, though, on weekdays the car park although big, fills up pretty quickly.
Another alternative is to go down the M11 all the way to Woodford and follow directions to Walthamstow: come off at waterworks corner and follow Forest Road to Blackhorse lane station on the Victoria line, Blackhorse Lane station has a big car park that never entirely fills up.