Grass or dirt. I always thought it would be hard for the gardeners to trim around. I don't remember if they are space suit foot prints. Shoe prints or little barefoot prints with toes. I think shoes. It was a long tour day and to be honest, I think it was like 7 am and that was what, 4-5 am our time? By that point in the day I was already tuning out. Guy giving the tour was the President of Purdue, former governor of Indiana. Republican. I knew that because as he drove thr golf cart he didnt' stink like socialism.