Hi. I have recently watched an interesting Youtube Video where a young French couple converts a cave into a home with a rental unit. This is an example where innovation is not necessarily in making a new product, it is more of using something which currently exists and using it in a unique and innovative way.
The video is just over 17 minutes long and can be found here.
The featured image (not related to the video) is from http://www.anityacavehouse.com/wp-content/uploads/2014/06/DSC_5603.jpg