It might be the most obviously unfinished motorway in the whole UK, let alone in London. The M23 was supposed to link London with Crawley - but its urban section was a problem that couldn't be solved.
It was the UK's only single-carriageway motorway, and twenty years ago it ceased to exist. This is the story of the strange fascination it held, and of my place in history.
If you've ever been on the M62 across the Pennines, you'll know the one. It's the huge arched bridge 120ft above the road. And this is what it's like when you're standing on top of it!