An investigatory project is basically any science experiment where you start with an issue or problem and conduct research or an investigation to decide what you think the outcome will be. After you've created your hypothesis or proposal, you can conduct a controlled experiment using the scientific method to arrive at a conclusion.In order to conduct a great investigatory experiment, you have to ask an interesting question and be able to conduct an experiment that can hopefully answer that question. The harder and more intriguing the initial question is, the better the resulting investigation and experiment will be.I've listed a few examples below of some of the best investigatory experiments out there, so hopefully you'll have no problem coming up with an idea.