Yep, in a Discovery not on a bike. We went up route 35 from Gulfoss upwards. Its an easy enough drive up a pretty well graded dirt road so no hassle really - theres even a twice daily bus service that runs.
More tricky is the longer route between the two large ice caps which we didn't try. Had we been in convoy with more than once vehicle we might have given it a go.
Awesome scenery though and well worth doing so.