Floor and north rim of Dokka Crater. Dokka Crater is 52-kilometers in diameter and located in the north polar region of Mars. Its interior is presumably a remnant of a former polar cap with larger extension, so it could provide valuable information about the past Martian conditions. (see: Analysis of Frost Inside and Around Dokka Crater in the North Polar Region of Mars)
HiRISE Picture of the Day archive. [More at links]