Here's a little nugget for fans of transport trivia. If you ride the Elizabeth line out to the west, you can pass through three ceremonial counties in three stops.
West Drayton is at the edge of Greater London (and Oyster validity); Iver is in Buckinghamshire; and then the remaining stops beginning with Langley are all in Berkshire.
We don't think it's possible to do this anywhere else on the tube map*. The closest elsewhere is the north-west section of the Met line, where you can jump from Greater London (Northwood) to Bucks (Chalfont & Latimer) fairly rapidly, but passing through three Hertfordshire stations.
The three-county anomaly has been sitting there on the tube map since 2019, when the Reading branch of TfL Rail first appeared, but we only just noticed it thanks to the Elizabeth line rebrand.
So, for anyone planning on visiting all the English counties in the shortest time possible... this would be a good place to start.
*Note for pedants: The Elizabeth line, of course, is not officially a tube line. However, the famous diagram published by TfL is titled the "Tube Map", even though it includes several transport modes that are not the tube.