This guy has built what he claims is the world smallest V12 engine.
For the uninitiated, here's some info on the V12 engine configuration. It's basically just like the engine in your car, just with more room to let gasoline explode.
For me, the most impressive thing about this clip is watching him craft the engine pieces out of the raw metals he acquired. I've seen more than a few videos of folks cutting crankshafts in lathes, but to see one that fits in the palm of my hand is absolutely fascinating.