My husband and I are huge Andy Goldsworthy fans and often incorporate elements of his work into projects for the children. We were in Nice, France last December and the rocks on the beach are (mostly) gray with white lines running through them. We set M&B to collecting and assembling their rocks to form a seamless circle of white.
PS. a friend of mine mentioned that he had not heard of Goldsworthy before reading this post, so I’ve added a link to an incredible documentary about him. Both M&B (ages 7&5 enjoyed this one, so it’s something you can watch "en famille".