The Atlantis Chaos is a region on Mars splattered with small peaks and troughs, the result of erosion of a once-flat plateau. Thanks to the magic of technology (and the ESA's hard work), you can take a virtual flight over the area.
The ESA's ride-along description paints an impressive picture of the area:
Explore the Atlantis Chaos region of Mars, in the Red Planet's southern hemisphere. The video showcases a myriad of features that reflect a rich geological history. The tour takes in rugged cliffs and impact craters, alongside parts of ancient shallow, eroded basins. See smooth plains scarred with wrinkled ridges, scarps and fracture lines that point to influence from tectonic activity. Marvel at 'chaotic' terrain — hundreds of small peaks and flat-topped hills that are thought to result from the slow erosion of a once-continuous solid plateau. This entire region may once have played host to vast volumes of water — look out for the evidence in the form of channels carved into steep-sided walls.
To put things in perspective, the top image also shows the Atlantis Chaos: it's the small, pockmarked region in the centre of the image. Colours show elevation, with the purple craters being the lowest things, rising to the red and white mountains. Atlantis's canyons and hills are barely enough to change the colour.