Mars photos from NASA APOD.
You must ENLARGE these photos to maximize awesomeness.
Thawing sand dunes:
Barchan sand dunes blown by the wind take a liquid aspect:
Landslides of black sand create the impression of a surreal forest of ebony yucca trees:
This crater, the Echus Chasma, is hypothesized to have been one of the major water sources on Mars. These cliffs are ~4km high and were possibly carved out by running water. At one time this may have been the greatest waterfall in the solar system:
Martian landscape marked by mysterious streaks of black sand:
Strange white finger-like rock formations revealed at the bottom of an impact crater:
A weird 150m-wide pit in the side of a volcano. Infrared thermal signatures suggest this is a very deep hole leading to an underground cavern system. Several of these pits have been identified: