The whole world is opening before you now. I already said to War: visit some place you wouldn't think of usually. Some small town in Poland. Some mountains in Montenegro. A ghost town in Germany (if there are even any; I'm just wildguessing). That bar all the locals are talking about but no guide tells you of. Roads best lit, while safest, are also the most boring. Man, I'm jealous of your travel opportunities. For how long is your trip?
There's probably a few in the east, or places that will soon be demolished for open pit coal mining. That said, all I see on wikipedia are troop exercise places.A ghost town in Germany (if there are even any; I'm just wildguessing).
UK has quite some history to uncover, all over the place. It's a much smaller country, so I presume your endeavour can take a deeper turn here and there. Stay curious, and you'll be able to find the most exciting things in the most ordinary places.