Do you have some kind of interesting mind games that you play when bored?

I saw Top Gun when I was five. When I got six my mom told me I'm going to grow too tall to be a fighter pilot. Then I thought I'd design a fighter that I could fit into. When I was seven I already though that airplane engineering was cooler than being a fighter pilot. Then I learned to read and I wanted to be a writer and aircraft engineer and loads of other stuff too. And I kept inventing new characters to my book and inventing new designs for fighter aircraft. Naive yes, but the last time I think I was bored was at age eleven. And nowadays I'm really good at imagining stuff in 3D. Few of my current things are that fighter thing(I already forgot, but it started again when I read about diamond box wing), optimum medieval castle(given the technology of that time), what is problem with our school, how could I manufacture a rifle barrel without drilling a hole, how democracy could be improved and what will happen when singularity becomes self aware.

So do you have cool ones?