My interest in offroad riding was sparked by family tales of ancient paths over the mountains. It’s kept me on the bike most of my life.
If you look at a map of old settlements and pick a few in the same area, even if there are no current tracks shown, you can often guess at the route they may have taken.
The fun is then going out on the bike and trying to find if you’re right. A bit of bushwhacking may be required. 🙂
In Scotland this is a useful resource, as are the old OS maps.
http://www.heritagepaths.co.uk/pathdetails.php?path=145
Or going back further, I find this one useful.
https://www.pastmap.org.uk/map
It doesn’t show the routes, but if you look at long abandoned places which were likely to have a sizeable population around them such as duns and forts, you can often find remains of tracks connecting them – but rarely a continuous one because of agriculture and forestry.
One thing to keep in mind is that flat land near waterways could well have been bog, so look a wee bit higher up the contour line.
Of course, a lot of the more obvious routes have been in continuous use and are now roads, but there’s still lots untouched in recent times.