What is the best idea you’ve ever had so far?

Our house doesn't have a functioning air conditioning system. We've got a heat pump, but it's been broken for a few years, and we can't afford to get it fixed. A couple months ago, I mentioned to my mom that when I lived with a couple of friends in a similar situation, we would put blankets up over the windows during the day, and open up the house completely at night.

We're not using blankets, but we now have black fabric over the windows in the living room that don't open, and it's keeping things nice and cool in there.