There is the hot dry kind that burns the soles of your feet as it shifts beneath you, leaving a crater. There is the hard, wet sand just beyond where the ocean stretches out it's waves. There is the sand actually on the edge of the surf, which gets washed away around your feet when a wave sweeps around you, and the sand that has a thin layer of standing water on top of it which your feet will sink into if you squiggle them around a bit. And there is also the crusty sand, which has a layer of salt over the top like the caramelized top of a tasty creme brulee. If you walk carefully, you can avoid leaving footprints on this kind of sand, but if you don't balance your weight evenly on your feet, they will break through the crust to the warm dry sand below. This is my favorite kind, because I can walk without leaving a trail, but it requires physical and mental concentration. When walking down the beach I can choose a path, if I'm careful and lucky, which will allow me to stay on sand hard enough to support my weight without breaking.
Perhaps my love of sand is silly, but to me it's really amazing that tiny grains of rock can behave in such different ways based simply on temperature and the amount of water mixed with them. The endless variations of nature are truly incredible.