How much by dirt trails…

[othermike]

Hi all,
Perhaps this question ought to be somewhere else on the hub but not sure where to put it.
I’m really into the off-road side of travel and wondered how much of the world can be navigated via dirt trails alone? Would be possible to link the world up like the TET has done with Europe. I’m getting that some countries, off road is forbidden altogether or there are not trails to navigate.
I have been to “the Stans” and loved that Tarmac was rare and could be avoided. Where there was a dirt road (full of corrugations) the dirt trails either side were much better and fun….
Of course, a tarmac road is such a relief when shattered and you need to get somewhere, but do wonder about the opportunity to ride the world by dirt where you can.
A pipe dream at the moment….