I was just looking at a map of the UK, and realised that I've been as far north as Dornoch and at least as far south as Plymouth. It seems like such a waste, somehow, to have travelled so much of the length of the country but not quite to have done the whole distance. So I'm going to do it. I don't know when, and I'm not going to try anything rash like walking it or cycling it, but I am now determined to see both ends of Britain.
I'd do Ireland too, but the drive from the border to Dublin is just so boring. No challenge is worth that.