Those who know even a little of the history of the Central Line east of Liverpool Street station will understand why this could be possible, whilst those who only understand an Underground railway (or "urban metro") in terms of a transport network which would only serve densely populated built-up areas will be somewhat surprised.
Filmed in June 2016, horses in a field adjacent to the Central Line between Barkingside and Newbury Park stations peacefully graze whilst a 1992 tube stock train passes by.
ps: my above comments are because some people have expressed surprise at what I filmed.
pps: on another day I saw cows in that field, not horses!
I'll admit the first time I watched it, I didn't understand what was so special about it, it didn't click at all how strange it is that all but twenty minutes ago that train was deep under Oxford street.