It's hard enough for humans to slog through soft sand, how well could a robot possibly handle that kind of terrain? Pretty well, if it's the prototype designed by Chen Li of UC Berkeley and Tingnan Zhang and Daniel Goldman of Georgia Tech. You can see one of their designs below:
You won't be surprised to learn that the scientists used lizards and insects for inspiration in building their robot. In particular, they were interested in how animals make multifunctional usage of their limbs to cope with different situations. To that end, they made their robots struggle through sand, glass spheres, and even poppy seeds.
The authors expect their research to pay off in building better robots for both exploring other planets and for search and rescue missions here on Earth. However, those are just two of the myriad uses for a robot that doesn't require solid ground for movement.
You can see Goldman explain the results below. Yet another use for 3D printing!
Li, C., Zhang, T., & Goldman, D. (2013). A Terradynamics of Legged Locomotion on Granular Media Science, 339 (6126), 1408-1412 DOI: 10.1126/science.1229163.