Clearly I know nothing at all about you or your intentions but if you are going to Lewis/Harris then really do make the effort to get away from the roads and tracks and get out onto the more remote bits of the moor. Clearly common sense and some ability to navigate are required but that comes with any wander no matter where you are. I would say 99% of visitors are never more than a few hundred yards from their car and there is so much to see that it is a waste to go all that way to sit by your car, you might as well got to a railway station car park
Here are a few suggestions for some Lewis walks, with plenty photos, and if these get anyone started heading away from the road then it is worthwhile:
http://www.7south.co.uk/Localwalks.html
Another point is that there are lots of interesting bryophytes on the moor right under your feet and they are well worth a look, I must do another post with bryophyte photos, it might sound crazy but they make great photos and are interesting things.