In the middle of Parker's Piece (no relation to the Thunderbirds character) in Cambridge, stands a lamppost. The only lamppost on the common, a beacon and a reference for anyone walking there at night. A bit like the lamppost in Narnia. A lot like the lamppost in Narnia in fact, as it serves as a boundary marker between the university and the town, two worlds with distinct notions of reality. That's one theory behind the name, the Reality Checkpoint.
Another theory suggests one should use the checkpoint to assess their clarity when going back from the pub, and this view certainly calls reality into question... Not to worry, the Ferris Wheel is just being dismantled.
This ornate lamppost has been restored in recent years, and improved with a Dinky Door. Well, I say "improved", but the note on the door says "on holiday, please check reality yourself"!