Temporary labyrinths could also be created on the beach and the washed away with the next tide. The robot would do the hard work of lay out and drawing and people could enjoy watching it done and then have the fun of walking the finished product.
Disney has been working to develop a sand drawing bot for fun and artistic purposes. Its fat tires prevent the rolling bot from messing up the image being drawn. Check it out in the following video. It would be fun for all these ideas to come together!