Rocks are cool enough on their own, but with just a little help you can make them even more useful. Add a little glow-in-the-dark paint, for example, and you can create a glowing guided walkway.
Yumi Sakugawa always comes through with some interesting ideas. Glow-in-the-dark rocks could be very useful planted alongside a dark driveway or walkway. You just need some glow-in-the-dark paint (available in several colours) and whatever rocks you want to use. Check the link below to see what other cool ideas Yumi has for using rocks.
8 Cool Things You Can Do With Rocks [WonderHowTo]