There's the "uber sleep" method or whatever it's called. Made the rounds in my circle of friends in like...2007ish?

Basically you force yourself to only take 4 15 minute naps a day. A utterly hellish thing to do, but eventually your brain figures out that you've decided to terrorize it and will instantly dip into REM the moment you fall asleep, and you'll wake up feeling rested and only need to sleep an hour a day.

I personally tried this for a bit and it kinda sorta works, but it's awful to get started, and the first time you sleep more than 15 minutes you're going to break the trend and revert, and who knows what long term effects it has on people.

Sleep in general is one of those really interesting areas of biology that we still don't get.