I was looking for somewhere to post this, but apparently there's no suitable thread for it yet.
Having searched for a polar sightseeing flight (AB1111), I have just stumbled upon a glider over mainland Denmark which has somehow ended up on Flightradar24.com.
Apart from that, I have noticed the occasional private prop and helicopters flying from Scotland to oil rigs in the North Sea.
I found this interesting, so I thought I would share. Which unexpected flights have you found on the site?