Well, I've already done something spontaneous!
I visited my mum in Brighton (well, Hove, actually) last week, and a couple of spontaneous things happened.
Firstly, I had my shoes shined by a real shoe-shine-guy! Not something I've ever had done before, and not something I'd normally do, but I decided 'Why not!' It was rather fun - the sensation of the brush and cloth through the boots was quite different, and the chap was interesting to talk to. It was a real 'spit & polish' too!
The other spontaneous thing I did was ride the Brighton Wheel.
I've never been on the London Eye, or a Ferris Wheel or anything like that, as I'm a bit nervous about heights, but I decided to give it a whirl. The views across Sussex were lovely, but I was more taken with the view over the English Channel.