Google MarsClick here to start exploring Modified Mars in Google Earth. This may take a minute but believe me, it's worth it. Make sure you turn off "borders", "roads", "restaurants" and other Terran layers in the Layers-window, left below in Google Earth, to avoid an odd mixture of Earth and Mars.
You need, of course, to have Google Earth installed on your computer. If you don't have Google Earth, you can download it here for free. Alternatively, you can explore Modified Mars as a "flat" map.