For most of the history of London’s underground rail network it had a Circle line. From 1884 to 2009, it was possible to get on a train and then spend your day spiralling round and round the same loop around central London, returning to your starting point every hour or so.

But then in 2009, the Circle extended to the west and became a tea-cup. You’d start in Hammersmith, and travel once round the loop via Edgware Road, Liverpool Street and Embankment, before coming to a halt at Edgware Road once again. It’s still known as the Circle line on the map; an actual circle it ain’t.

There are, however, a number of other loops hidden in London’s rail map. They’re not true circles – you can’t just keep going round and round them forever. But there are, nonetheless, parts of the network where you can remain on a train and find yourself back at your starting point, without ever doubling back on yourself.

By my count, there are eight. If I’ve I missed any, do let me know.

Let’s start with an easy one:

Hatton Cross to Hatton Cross via Heathrow Terminal 4. Happens all the time.

While we’re on the tube:

It’s quite rare for trains to go all the way round the Central line loop: generally they run to Hainault via Newbury Park, or on occasion, to Woodford via Hainult; mostly, the northern section exists almost as a sort of branch line.

But just occasionally, you can get on a train at Leytonstone, travel via Hainault and Woodford, and then find yourself back where you started.

Okay, now for the less obvious ones.

Tramlink, which serves London’s deep south, has a Heathrow-style loop in central Croydon: trams from Elmers End (route 1) and Beckenham Junction (route 2) go round it and end up back where they started. That gives you a choice of routes to get from East Croydon to East Croydon, should you feel the need.

Light green, to the left.

Just up the road, the Thameslink loop similarly gives you a choice of options to get from Streatham to Streatham: clockwise, via Sutton and Wimbledon; or anti-clockwise, via Wimbledon and Sutton.

It’s the purple one.

Oh how the days must fly by.

Okay, now we’re getting to the real obscure ones. This map of part of the South West Trains network contains not one but two hidden circles:

The red bits.

Firstly, there’s the Kingston loop, which enables trains to travel from Clapham Junction to Kingston, Richmond and back again – or, if anti-clockwise is more to your taste, vice versa.

The result is that, if you’re at Strawberry Hill and you’re trying to get back to Waterloo, you have a choice of directions (which is lucky as there are only two trains an hour each way). It’s marginally quicker to go via Richmond (34 minutes) than it is via Kingston (42), mind.

The other is the Hounslow loop, which does much the same but on the north side of the river. Richmond, then Hounslow, or Hounslow then Richmond; either way you can go from Barnes to Barnes in just over 40 minutes.

Departure boards, incidentally, tend to show some trains as terminating at Hounslow or Barnes Bridge, presumably in an attempt to prevent people from getting on one going the long way round the loop. Spoilsports.

Lastly, there’s the various Southeastern loops:

In practice, only two of these are in regular service. You can get trains that go via Bexleyheath and Abbey Wood, and trains that go via Crayford and Abbey Wood; but at present, best I can tell, there are no scheduled trains that run via Crayford and Bexleyheath.

Nonetheless – while London may not have a proper circle line any more, it has no fewer than nine different loops, where the same train or tram will take you from one station to itself without ever turning round.

So, now you know.

Right, that distracted me from the election for a whole hour. Now, how am I going to fill the next seven weeks?

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and also has a Facebook page now for some reason.

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All maps courtesy of TfL.