There are two places in London where a '20' postcode rubs up against a '19'. Here's one of them.
SE20 is Anerley, with Penge, plus bits of Beckenham. SE19 is Upper Norwood and Crystal Palace.
The SE20/19 borderline runs along the railway and round Crystal Palace Park.
You can probably guess what I did armed with this information. I went for a walk.
One end of the SE20/19 interface is at the pedestrian entrance to Crystal Palace Park. That'll be SE26 on the other side of the road, but we have no interest there. The gates are far less spectacular than they ought to be, just a gap in a brick wall and some pansies in planters. Up the slope, past the car park, the new cafe is fast arising on the site of the old. It looks like a gingerbread house waiting to ensnare lost children, but the tiles are in fact meant to represent dinosaur scales so waifs and strays need not be sore afraid. It should be opening this year, once the encircling works are stripped away, and will be run by the same team who run the cafe at the station we're heading to next.
The postcode boundary follows the edge of the park, with the lake in SE19 and the villas on Thicket Road in SE20. Given the number of seagulls perched across the pedalos, they'll need a good wipedown before the summer season kicks off. Crystal Palace's not quite biologically correct dinosaurs patrol their own island, which may soon gain a bridge thanks to a recent fundingcampaign (although only to permit supervised tours and activities so don't go getting any over-optimistic safari dreams). The beasts have not lost their ability to draw the crowds, though if anything it's now the adults who are most excited as they line up their pseudo-prehistoric selfie backdrops.
At the arched bridge the SE20/19 boundary switches from road to railway, now following the Overground, but still running along the edge of the park. "Just leave me," says Elliot, who must be all of six years old and is standing resolute in a multi-coloured anorak. "Just leave me on my own." I am impressed by his calm, collected, tone of voice, as if he has thought this through rather than simply throwing a tantrum because recent family time has been too much. His mother stops and talks to him politely but firmly, explaining that she can't leave him behind because it's not allowed and anyway she doesn't want to, and I think I've worked out where Elliot gets it from.
Outside Crystal Palace station a woman in a knitted Christmas pudding bobble hat has her finger in a newish copy of the Capital Ring guidebook, while her partner looks up the routes of local buses on a poster. They've come prepared for a proper hike, with walking boots and rucksack, although the lack of clinging mud suggests that Beckenham Place and Cator Park did not deliver. Officially the station is in SE19, but the boundary comes in up platform 6 and back out down platform 1 which leaves Orchard Grove (the cul-de-sac up the middle) in SE20. If you're counting.
The station remains vastly out of proportion to current usage, reflecting instead passenger throughflow from its glassy exhibition hall days. A broad staircase sweeps down to the farthest platform, which ought to be perfect for making a dramatic entrance except it's closed off Do Not Alight Here. A small toddler walks slowly up from the Overground, making each step harder that it should be, leaving her father wishing they'd taken the lift instead. Brown and Green in the Victorian ticket hall isn't a cafe, it's a 'brunch kitchen', but BestMate nevertheless highly rates its coffee. And as for the remaining half mile of the SE20/19 boundary, you can only follow that by taking a train from platform 2 as far as South Norwood Lake, but that's in SE25 so we don't care about that either.