It bears none of the symbols of the rest of the network: crowded carriages, gruff commuters, regular services, and mile upon mile of darkness. Instead it operates at a pace and in a manner entirely divorced from its parent.
Trains are infrequent. Carriages are almost empty. You can sit in a station for ages, entirely at the whim of whoever is - or isn't - at the controls. And you pass through landscape so beautiful and undisturbed as to suggest you aren't so much in a different county but a different country.
North of Moor Park the line divides yet again, with one branch curling off towards Watford. To ride this service is like taking a Sunday afternoon excursion along a miniature railway. You pass through fields and forest, with trees bending right over the line to form a dense tunnel of foliage. I saw foxes, hares and squirrels alongside the track. It really is as far removed from any notion of an Underground railway as it's possible to get. Here's a photo of the line I took from a bridge outside Croxley station:
The Metropolitan reached here in 1925. Initially the station was named after the village: Croxley Green, a charming place and thoroughly, unashamedly, rural. It reverted to its present title after the Second World War.
The Herfordshire countryside intrudes right onto the platforms:
After Croxley it's but a few miles and minutes to Watford, though the station, such as it is, is no way a direct link to the town. It sits far out on the edge of the suburbs and resembles, much like Mill Hill East, a terminus by default. Originally the line was to have continued into the town centre, and recently plans have been revived to try and achieve just that. For the time being, though, it's a curious cul-de-sac into an unlikely port in the middle of nowhere.
If you take the other branch from Moor Park you're following mainline services towards Buckinghamshire. As late as 1961, Rickmansworth station was the point at which Metropolitan line trains bound for London switched from steam to electric locomotives. Up until then, if you wanted to travel north of here you'd find yourself being decoupled from your swish diesel service to a wheezing, hissing steam engine hailing from the back end of 19th century. Electrification of the line was seen as less of a priority, clearly, in this backwater of the Underground.
Rickmansworth, like many of its neighbours, seems to pride itself on its horticultural exhibitionism, and so it should:
...is even more at one with nature:
By now I was passing through stations that felt untouched for over 100 years, where the arrival of a train seemed almost an inconvenience, disturbing the tranquil inertia and unapologetic calm.
Chalfont and Latimer opened in 1889 to serve the numerous similarly-named, quaintly-titled Chiltern outcrops of Chalfont St Giles, Chalfont St Peter and Little Chalfont. Entering the station was like going through the door of a village hall.
Here the line divides yet another time, offering a choice of destinations: Chesham or Amersham. Chesham is a dead end, served during the day by a desultory four-carriage train that goes back and forth, back and forth every half hour or so. It's possibly the least integrated example of public transport on the whole network. The train leaves when it feels like it and arrives likewise. I sat on it in Chalfont and Latimer for 25 minutes before it moved an inch.
Chesham itself, opened in 1889, is a real end of the line place. It has the longest distance between adjacent stops on the entire London Underground, and is the most westerly station there is.
Unmanned, somewhat ill-kept and not a place to want to linger, its only appeal - when I was there - was its view across the Chess valley towards the rest of Buckinghamshire.
Its neighbour, Amersham, is the resting place of all through-services on the Metropolitan. By dint of being on a mainline route it's nowhere near as disheartening as Chesham, but you're still at the mercies of the system as to when the next London-bound train will be leaving. When I was there, campaigners were handing out leaflets to try and stop the planned closure of the ticket office.
I might have had more sympathy for them had they not made the central point of their argument the rather fusty claim that the Oyster card was "complicated". It's nothing of the sort!
As John Betjeman took great trouble to point out, the Metropolitan didn't always end here. Originally services continued, on to Great Missenden, Wendover, Stoke Mandeville and Aylesbury (up to 1961), and also beyond, even further into Buckinghamshire, to Waddesdon Manor, Quainton Road, Granborough Road, Winslow Road, and Verney Junction (up to 1936).
The latter was conceived by captains of industry to be one of the great interchanges of the country, on a par with Crewe or Clapham, with trains from the north joining the Metropolitan to rush all the way down to London, through the city, onto the coast and, spectacularly, under the sea to France.
Such ambition seems preposterous nowadays, at a time when it takes almost 20 years to merely get agreement to build a single new railway to run from the west of the capital to the east. But at least those engineers and planners had the inclination to dream.
They also had the foresight and willpower to extend the Metropolitan deep, deep into the shires outside London, thereby allowing the city's residents and workers an ongoing chance to escape into the restorative meadows of Metro-land.