I'm not entirely sure why. Perhaps it was because I would be so far from where I lived. Perhaps it was because it looked a long way on the map. Perhaps it was because I was heading towards an airport, where I would be trying to take photographs and not look suspicious.
There have been tracks down this way since 1883, when the Metropolitan District Railway (now the District Line) opened a service to Hounslow Town. The Piccadilly began running trains during that decade of uber-expansion: the 1930s. District Line services disappeared 30 years later. The last piece in the jigsaw, the extension to Heathrow, only materialised a couple of decades ago. Indeed, part of it is still materialising today.
South Ealing, one of only two stops on the entire network to boast all five vowels in its name (I have yet to visit the other), squats by a pelican crossing at road level but opens out into a huge, recently refurbished cavern inside.
It's only just down the road from Northfields, or Northfields Halt as it was originally called. Or Northfields and Little Ealing as it was subsequently called. Either alternatives, I think, would improve the character of the place today and match the regal pretensions of its design (another Charles Holden effort).
Holden's tentacles extend down the line through Boston Manor and Osterley. These are fantastic creations, enhanced - inevitably - by the kind of brooding skyline that accompanied me on my trip. It's the towers that do it. They reach up into the firmament for no reason other than they can. The one at Boston Manor has an illuminated strip that rises above the tower itself, challenging the sky to do its worst.
Osterley, though, goes one better. Here the tower is capped by...another tower, poking up even higher, which feels like it's almost scraping the clouds. How many people pause to look up at this edifice when they're entering the station? Depends how many people have got the time and the inclination, I suppose. Probably not enough, though.
The trio of stops in Hounslow turn out to have vastly contrasting, confusing histories. The line used to terminate here, at a station called Hounslow Town which no longer exists. Then it was extended to Hounslow Barracks, which is now Hounslow West. For a while there were no, as there are now, Hounslows East and Central. Central turned up in the guise of Heston and Hounslow, but to the west of Hounslow Town. Then a new Hounslow Town opened, which is now Hounslow East. Following all this?
It's not that important. Nowadays Hounslow East, the first you come to when you're travelling towards Heathrow, is a real shock: uncompromisingly modern and completely at odds with its surrounding neighbourhood. There's no real point for it to look this way, other than to make a point.
By contrast Hounslow Central looks like a village shop...
...and Hounslow West like a university library:
No prizes for guessing who designed that one.
Here was where the Piccadilly Line ended for a very long time. Since there has been a civilian airport on the site of Heathrow since the Second World War, it's surprising now to think there was no Underground link until 1977. Hatton Cross only opened in 1975, acting as a temporary terminus until the final bit of the line was laid two years later. This last stretch of the Piccadilly was simply dug just under the ground then covered back over, in the same way the very first Underground lines were dug an entire century earlier.
Hatton Cross is a horrendous place. The station is like a warehouse: cold, vast, ugly, dumped in the middle of nowhere, and with absolutely no concession to anybody desiring to do anything other than pass through en route somewhere else.
Trains from here run either straight to Terminals 1, 2 and 3, or the same destination via Terminal 4. Or at least they did when I was there. In a matter of days this is set to change, when Terminal 5 opens and - hooray! - all the London Underground maps across the city will need to be replaced.
Terminal 4 was opened in 1986 and is a far more obvious and logically-designed place than its neighbour. It took me only a few minutes to get up from the platform and into the terminal arrivals lounge, a route clearly signposted and easy to use.
1, 2 and 3, originally called simply Heathrow Central on its opening in 1977, is a completely different matter. I didn't know where I was going once I'd left the station, first ending up in a bus depot, then outside with a bunch of smokers. All I was looking for was the main station entrance. This was as good as it got.
There's no way of getting directly from Terminals 1, 2 and 3 to Terminal 4 by Underground. You'd have to go back to Hatton Cross and start again. The line runs one way only, hence why there's only one platform at Terminal 4 station. Heaven help you if you need to nip to Terminal 4 quickly from 1, 2 or 3.
Believe it or not, this was my first proper visit to Heathrow. When I was very young my family went on a day trip on a plane from East Midlands Airport to Heathrow and back again - the height of sophistication and exoticism, I'm sure you'll agree.
Maybe it was that trip which gave me my fear of flying. I certainly recall being terrified at the mere notion of not having anything by way of solid matter underneath me. Anyway, since then I had never been to, or had cause to go near, Heathrow.
It's not a nice place. I felt as if my brandishing a camera around the place was being picked up by 100 security cameras. Despite it taking me hours to get to, being something of a national landmark, and representing the end of my vast journey around the Piccadilly Line, I got out of there as soon as I could.