Once activated on Mars this year, the Opportunity Rover will make a try for a true marathon, or 26.2 miles.

Interestingly, when it first landed, scientists hoped it would go 600 yards ( or meters, for those Euros out there).

After overcoming various mishaps, like the failure of a drive mechanism on one of the front wheels that required scientists to drive the rover backwards, Opportunity only has a bit over four miles still to go to make a marathon distance on the red planet. I think they got their money's worth on this one.